They obviously know this. It has just been a matter of time for the contract to run out and for them to look at the feasibility of which networks would be best to get on when Verizon and the others would require new hardware and software to work. The decision they made in the beginning made sense at the time. But now things have changed and so will Apple as soon as they are free to do so, which should be this summer or sooner.
You can actually thank the French government for this. Them mandating Apple to end the exclusivity there is what opened Apple up to see that being on all carriers proves very beneficial for all involved! If that hadn't happened, I'll bet Apple would have waited till either the "world" chip comes out later this year, or till LTE since it is all compatible.
This announcement sure would make a LOT of people happy for a "one more thing" though!