I have a bunch of apps installed but the only ones I bought for my android device are utilities for rooted devices. But I did drop $5 for poweramp and $3 for a sexier voice for google nav.
I am probably not helping with the Android numbers. I still refuse to get anything from the market that costs money, I am still dubious as to how safe the Android Market is when it comes to using my card. Android Market probably lost a lot of money when Angry Birds was released for free. I suspect that game made a lot of money on the iPhone and everyone I know with an Android phone has it. I don't use the satnav as I still trust my TomTom a little more but if it ever goes wrong knowing I can pay £10 for a car mount for my N1 and use that is nice to know.
You are paranoid. The Android marketplace ties in with Google Checkout. Also, depending on your carrier, you may have the option of carrier billing.