Your guess is of based on the mistaken belief that those phones are all in the US. A great percentage of those phones are in Asia and Europe. That bloc of iPhones only add to Apple's bottom line through the initial sale not through an AT&T revenue stream going forward.
So, that said, why you would think Apple would want to stop modifying their firmware to "help" these iPhone owners that are off-shore is beyond logic.
Perhaps you could comment on that.

Read a little closer. I *do* acknowledge what you say I don't, and I quote directly from my own article, which is that "Many phones are also sent overseas where the iPhones may have yet to roll out."

However neither you nor I know the exact percentage that stays domestic or goes overseas. Judging by online forums I'd say plenty of consumers are making the point of trying to use iPhones that are unlocked here.

Whether it's 50/50, or what, I'd be curious to find out.

And yes, no matter unlocked or locked, it does add to Apple's bottom line. My point is that if Apple sold unlocked more readily without bricking them onupdates, they might increase domestic sales to people not ready to switch to AT&T and increase their bottom line.