This has long been debated, but figured I'd finally log just to summarize and add my two nuyen.
I am on the side that, regardless of RAI and what Bull says for his
Missions, RAW is that you get a defense roll. I will explain why below, but before I get there, please note that this topic is so heavily debated that it really falls under the purview of your GM. There really is no right nor wrong answer and the devs have pretty much refused to comment. The only official FAQ about grenades comes from a 4th edition FAQ saying that hitting the ground is easy but any moving target (even in the blast) should always be opposed which only lead to confusion as 4th edition was pretty straight forward on the subject of grenades and defending.
TARGETED BY AN AREA-EFFECT ATTACK
Dodging explosions is not as easy as it seems in the movies. Apply a –2 modifier when trying to defend against weapons like spells, grenades, rockets, or missiles with a blast or area effect.
This is one of the strongest and yet one of the most argued "proofs" of a defense roll. However, the rule survived an errata and second printing. This is not some leftover artifact, it is there for a reason.
DAMAGE AND PASSENGERS
*snip*
The exceptions to this rule are ramming, suppressive fire, and area-effect weapon attacks like grenades and rockets—these attacks affect both passengers and vehicles.
If an attack is made against passengers, make a normal Attack Test, but the passengers are always considered to be under Good Cover (this is in addition to the +3 modifier for being inside a moving vehicle; additionally, the Blind Fire modifier may apply to the attacker as the situation dictates). Passengers attempting to defend against an attack inside a vehicle suffer a –2 dice pool modifier to their Defense Test, since their movements are limited to the interior of the vehicle.
*snip*
So right there, we are told that all AoE attacks (including grenades) are against both the vehicle and the passengers. We are then told that the attacks are made as normal, but that passengers are always considered in Good Cover AND receive a +3 modifier to defense. While less applicable to a grenade going through an open window due to chunky salsa effect and obviously being a situation where the GM deems a defense roll impossible, it further supports the notion that AoE are defended against normally as no where does this section split the distinction between AoE attacks and other options other than to say AoE attacks target both passengers and the vehicle instead of one or the other.
The test is like that for grenades (p. 181): a Spellcasting + Magic [Force] (3) Test with scatter of 2D6 meters. Unlike grenades, you get to add your net hits on this test to the Damage Value of the spell, but only if you beat the threshold; otherwise the spell still detonates, but the hits are used to reduce scatter by one meter per hit..
This is an Indirect Combat spell, so its damage will be equal to Force 7 + Rikki’s net hits. Ganger 1 is a little out of it and only gets 2 hits. The second ganger is quicker with 4 hits. The three net hits make the total damage hitting the first ganger 10, while the second must attempt to absorb 8 points of damage.
Clearly, this section shows that Indirect Combat spells are like grenades with the test to hit, and unlike grenades as they get bonus damage from net hits. This is the only distinctions made. Then we get an in-game example of two gangers making defense rolls.
MISSILE PARRY
Cost: 0.25 PP per level
Activation: Interrupt Action (–5 from Initiative Score)
You can catch slow-moving projectiles such as arrows, thrown knives, grenades, or shuriken out of the air. When using this power, add +1 die per level to your defense pool against the attacker’s ranged attack test. If you generate net hits, you pluck the missile out of the air. You need to have at least one empty hand to use Missile Party.
RANGED COMBAT
Ranged combat is determined with an Opposed Test between the attacker’s Weapon Skill + Agility [Accuracy] vs. the defender’s Reaction + Intuition.
Net hits are applied to the weapons DV or used to reduce scatter in the case of thrown weapons and launched weapons[color].
Again, no distinction made. ALL ranged attacks are opposed tests.
COMBAT RESOLUTION
Shadowrun includes four types of combat: ranged combat (p. 173), melee combat (p. 184), astral combat (p. 315), and cybercombat (p. 226). All combat, whether it involves firearms, knives, astral attacks, or attack programs, is resolved in essentially the same manner.
Combat is handled as an Opposed Test between the attacker and defender. The exact skills and attributes used depend on the type of combat, method of attack, and style of defense, as described in each section.
There are only four types of combat. Grenades fall under ranged and therefore follow the rules for ranged attacks. And before the good old, "But you target the ground, not the people!" argument comes around...
BLAST EFFECTS
Grenades, rockets, and missiles are area-effect weapons, meaning that their blast affects a given area and any targets within it. The farther away the target is from the explosive’s final location—the blast point—the less damage it takes, because distance reduces the effect of an explosive’s blast.
There you have it. All within the radius of the blast are...targets of the attack.
The other defense I have seen about the "no defense roll" side is that Run&Gun added two defense options to grenades, so obviously you can't defend normally," to which I say....what?...
The benefit of
Run For Your Life/Dive On Grenade is that you get to immediately run and eliminate damage with distance without any roll to do so for 5 initiative.
The benefit of
Right Back At Ya! is that for 10 initiative and two tests, you get to eliminate 100% of the blast (also protecting your allies) AND make your attacker possibly suffer it instead.
Neither of those additional options eliminate the benefits of just rolling defense, but give more options other than, "dodge or die."
So, in closing, there are multiple places in the book that support or explicitly address that there is indeed a defense roll for AoE attacks and at least one actual example of how it is done in game. However, as far as I can tell, not one explicitly saying there isn't. Whether or not that is what was intended is unknown, but makes it pretty clear to me. You can form your own opinion and go from there. Again, it will vary from GM to GM.