(And by "General Public" I mean, people who aren't paying $30 a month for data transfers, and just using wifi instead.)
You can download applications over a wifi connection without any phone plan. For example, I recently removed an HTC Hero from my phone plan and was able to download applications to the phone over Wifi with no problem.... even though I could not make calls.
Since Android is not limited to phones or devices with wireless data plans, requiring a phone plan would not be possible for all Android devices.
Additionally, with competion in the works like Amazon's upcoming Android applications market, there will be too much disincentive for Google to require a monthly fee for market access.