I know that for the adventures I've written, my design philosophy has been fairly simple: it's easier for an experienced GM with tough, experienced, PCs to ramp up the difficulty, than it is for a noob GM with noob, softer, PCs to ramp difficulty down. At the end of every scene in those adventures is a "pushing the envelope..." paragraph or two with some suggestions for how to make it tougher, ranging from adding more guys, to suggested new stats, to suggested new gear, to other complications that could still fit the scene.
So the default threat level in them is fairly low. They're made to be easily runnable by any old random GM at a convention, who's running a table of 4-8 or so total strangers, who might have never played together before, might have never played Shadowrun before, and might even be running the archetype characters from the core book (hell, I ran Ancient Pawns for just two players, at one little local con). I set the bar low, because to me that's easier than having a "default" power level that's too high, and seeing a new GM try to flail and struggle his way through gauging the power curve and trying to alter it.
Now, I had nothing to do with the NPCs from the core SR4 book, because when it came out I was just another fan (and a fairly disgruntled one, some Dumpshock alumni may recall). But when I was putting my own NPCs together, ranging from go-gangers to Humanis thugs to Ork Underground door guards to a whole wiz gang, I went for smaller die pools instead of larger, and left it to the GM to ramp up the difficulty if he wanted. Maybe they had the same design philosophy a couple of years back, when making the default guys in the core rules -- in addition to having less options, because they only had the core book to play with.
