DHH is (and I use this term unironically) a visionary. And on top of that he had a keen enough political sense (and arrogance) to be able to deflect or mute criticism of Rails's early flaws.
Ruby is a slow, memory hog? Doesn't matter, developer time is worth more than machine time. Buy bigger machines.
Rails concurrency model sucks? Doesn't matter, fire up more processes!
These were real problems, which have been subsequently addressed in Rails (by and large, by other people in the community who cared about those subjects). But what was important about what DHH did was define a vision and aesthetic for what web development should look like (and please note i'm no DHH fanboy. I jumped ship during the Merb/Datamapper split), and kept on pushing on his priorities even in the face of legitimate criticisms of things he thought were less important.
So, Rails succeeded because DHH has sensible enough taste in terms of prioritizing concerns, and a strong enough user base to fix Rails's shortcomings.
I'm not as familiar with the specific battles over Gnome (partially because i'm on OSX, and also because i find the interlocutors in the Gnome discussion to be so furiously inarticulate), but the conflict really only comes down to two possibilities. Either the leaders of Gnome genuinely are shit designers and aren't meeting the needs of their community, or they're really terrible at politics.
That's a really important distinction to be mindful of. I'm not amongst their target userbase, so frankly I can't say one way or the other, but all of the complaints I've heard against Gnome's leadership are things that I as a user have never ever cared about (granted I haven't used Gnome in a while, but all the times i've used systems w/ Gnome installed by default in the past, i've been satisfied).
And really, if Gnome's leadership is so inadequate, i'm puzzled why a critical mass hasn't risen up and forked the community. That's really the ultimate vote of dissatisfaction.