it's not about how many iphones Apple sell because they make more money on the call charges which is why the phone is locked in the first place.
In the UK the phone costs £269 and the contract costs a minimum of £640 on top. Apple take a minimum of £162 on the 18 month contract itself and a massive 40% off all call charges after.
One iphone = £431 (minimum over 18 months) for Apple or $894
It's seems likely that Apple will have to give up the fight on this 1st generation of the locked phone eventually, especially in Europe but with profit margins higher on call charges than on the phone itself I have no doubt that Apple will try every trick in the book to continue making money from call charges.
I suspect that with the contracts between Apple and the worlds networks as well as the money these networks have invested in the iphone, Apple will not just release an unlocked iphone to the world just like that.
I have a feeling that the 2nd generation iphone will be locked and have some additional 'must have, can't live without' features that will render the 1st generation iphone as obsolete. By the time the 2nd generation iphone is release I suspect the 1st generation will be officially unlocked only for the cat and mouse game to start all over again with the 2nd generation iphone and the 3rd and 4th and so on.
But this is all speculation, only time will tell.