I would draw a line between the US Indie scene and the "underground"/hipster scene that produces acts like Gang Gang Dance. I'll admit that its a fuzzy one, but no more so than that in the UK.
hmm, there's indie and actual indie, american stuff like pitchfork seems to be a bastion of actual indie values really, but i agree in a sense its pretty stuffy too, usually deconstructing 50 years of rock with minute changes of faces and structure, numbers of intruments, vocals less vocals rhythms etc.
incidentally i went to see comets on fire last night, it seemed to be full of london actual indie mafia ie the staff at rough trade and berwick street places, then the greasy boys that hang about the counters all day, and then loads of americans, and not many other people oddly. They seem to be a typically pitchfork band, i didn't enjoy it at all, 4 men playing the same riff on a guitar whilst someone else seemed to drop some electronics which i couldn't hear .
It seemed and looked like a weird wanking competition to me, but at any rate, it was more adventurous than any english stuff that calls itself indie which is all in all the straight up regirgitation of 30 years or so of guitar based pop paired down into a blanded out form, with the odd exceptions and the odd people who excel at it.