True, but consider it this way:
MG makes a new map feature. GAE will probably impliment it sometime, but hasn't yet. I make a map with that feature, but having the same extension, it can now crash GAE (assuming it doesn't know how to handle this new feature). The situation also works in reverse. Or if by some random chance, some poor, unlucky fool who doesn't want to download MG for reasons unknown (perhaps MG is too big of a download for said person, and maps are his/her limit?) and thinking its a vanilla glest mod, downloads it, only to have a crash.
Of course, I see your point, but I still have the last word:
Cons:
[Insert sweet nothings here]
How hard is it to make a new extension? Not one bit.
