There's a huge difference between challenging and impossible, though. As far as I'm aware, an independent developer is completely barred from releasing anything on XBLA, PSN, or Nintendo without a huge investment and a publishing deal. You're shut out completely. The closest is XBLIG, which is so overloaded with garbage that nobody uses it. That leaves Windows/OS X development, which has all the problems of exposure/marketing, but with no unified storefront and no convenient or consistent way to handle payments.

I don't think the window's closing, I think it's just that the gold rush hype has died down. People are starting to realize you can't crap out anything they want onto the App Store and then automatically become millionaires. I wish the best of luck to anybody trying to make a full-time living off of it, but there's still no way I'd jump on without supplemental gigs as a possibility. But then, I wouldn't quit my job and work full-time on my first novel, either; that doesn't mean that prose is dead.