Really that's a pittance. And it'll keep people from blatantly spamming the App reviewers with garbage.
Also it helps pay for the reviewing of apps, although they still take a loss on running the appstore, last I heard.
No need to imagine: http://www.android.com/market/
And the new appstore doesn't stop anyone from hosting their OSS on github - even for Macs. The appstore is for the average user; github is for the better than average programmer.