I've always found that whatever you say about indie rock, it is the most inclusive genre or title for anything. It doesn't pin you down too much, like other labels would. It's just newer, it has less baggage.
What's cool about indie rock is that one band can do effectively the same thing as another band, and one band nails it, and the other one doesn't. I like that elusiveness.
Now that the generation that grew up on '80s indie-rock has attained influential positions in the culture, that music is the new yardstick. And that will shift yet again some day.
To begin with, the key principle of American indie rock wasn't a circumscribed musical style; it was the punk ethos of DIY, or do-it-yourself. The equation was simple: If punk was rebellious and DIY was rebellious, then doing it yourself was punk. 'Punk was about more than just starting a band,' former Minutemen bassist Mike Watt once said, 'it was about starting a label, it was about touring, it was about taking control. It was like songwriting; you just do it. You want a record, you pay the pressing plant. That's what it was all about.'