Would it be reassuring if I told you I own the book and am quite familiar with it?
I'm not sure...
It is suggested that it be advanced very so often. That said, level advancement is not a necessity for a level-based game. AD&D would still be level-based even if you froze the characters at 10th level. E6 is level-based, even if you stop gaining levels after 6. If you run a Pathfinder and you use the "gain a level when I say so" method, you are running a level-based game, and rather similar to the default M&M level advancement system, at that.
A character gaining a level is the same as changing the campaign framework?
In a level-based game, characters are on a limited, mathematically specific tier of ability, which is supposed to make them roughly equivalent.
Ok, so every roleplaying game is level-based then in your opinion?
In HERO, for example, the level is set by the number of character points you get (standard heroic, powerful heroic, standard superheroic, etc - that's roughly the same as the PL of M&M, especially if you also use the recommended caps for OCV/DCs/skill checks and so on).
M&M is that. You can't get above X attack, X skill ranks, and so forth in D&D 3e, for each specific level, and you can't in M&M either.
Well, I can understand why you think M&M is level-based at least.
I do not agree with it, because I really don't think what you consider level-based, really is (or should be) level-based.
Basically, you see any limit/cap to a character's ability as a level-based limit.
However, there are two fundamentally different things at work...
1) the level of the character
2) the level of the campaign
You say, both of these make a game level-based. I think only the first one does.
Bye
Thanee