The X1600 mobility and the 7300GT are very similar in performance. The reason for the change is that AMD now own ATi and Intel don't want Apple supporting them so Apple will transition over to Nvidia chips to suck up Intel's ass.
I'm sure Intel couldn't care less whether Apple uses ATI or nvidia graphics cards, because Intel doesn't make GPUs, and Apple uses Intel CPUs. If Intel dared put pressure on Apple to move to nvidia, which they never would because Intel hates nvidia just as much as it does AMD/ATI, Apple would just move to AMD, and the AMD CEO would be extremely happy.
ATI's graphics cards seem to be outstripping nvidia's. Yes, nvidia is the only company at the moment with a DX10 GPU, but everyone knows that ATI's R600 is going to own it, and will most likely defeat nvidia's mid generation upgrade as well. Add the fact that there are no DX10 games out yet, and we have everyone waiting for ATI's R600. This quite possibly includes Apple, as they wait for something to pair with dual Clovertowns in the new 8 core revision of the Mac Pro.
Apple will always use what it deems best for the user, and what it deems best for its profits, which are inevitably one and the same. If ATI's cards are the best, Apple will use them, as they always have, and vice versa.
The idea that Apple will only use nvidia's cards in the future to "suck up Intel's ass" is a stupid, ignorant, trollish comment.