A single die system is can be more intuitive to new players, because it's easier to determine the probability of an action's success or failure. Needing a 16+ (or 5-) on a d20 gives you a 25% chance. A +2 gives you a 10% difference.
If they've never played a system with dice pools before, the whole system of hits, net hits, thresholds, and limits will be daunting, and building a character will be more frustrating than it needs to be if they can't reasonably judge how many points they will need in a skill to feel competent.
You (probably) take these things for granted, but they're not universal.
This. Exactly this. I can attest to some RL experience in this situation. I tried to get my D&D group into Shadowrun one of the times when it was my turn to take the DM's chair, and the look on their faces when they realized that I was the only person who had nearly enough d6s was pure culture shock. Afterall, in D&D you don't really need more than 6 or so d6s unless you're a spellcaster throwing things like Fireball around, or you're a high-level Rogue doing sneak attack. When they see me with 24d6, it blew their minds.
As far as Mutants and Masterminds is concerned, I've played it in several editions, and in several different campaign types (superhero, fantasy, sci-fi). It is a very adaptable system, and you can easily apply it to many different genres. Personally, I like Hero System better, for the more tactical feel, but again, being a points-based, effects-based system, it is something you can play in many different ways. I've never understood the hate some people have for d20, except by looking at indie music snobs who reflexively hate any band that signs to a label for 'selling out' and 'going mainstream'.
