And how many users of those budget phones even realize that apps exist, or will be willing to buy yours?
You make some significant assumptions here:
1. Android 2.3 is only found on budget devices, and
2. Budget device users do not purchase apps.
I don't have any data on assumption #2, but I can tell you that there are a lot of high end phones from 1 year to 1.5 years ago which are not getting the update to ICS / Jellybean. I happen to own such a device -- the TMobile G2x. Dual core, all around powerful hardware -- more than capable to run ICS and Jellybean. Much better hardware than Nexus S, which currently has ICS / Jellybean. But the G2x manufacturer (LG) will not update the phone to ICS and everyone is stuck with Gingerbread on this high end phone. So Android 2.3 does not automatically imply cheap phone.