The difference is that draft 2 will be able to interoperate perfectly well with the definite version of the 802.11n norm. As the name indicates, the 802.11n Draft 1 wifi in the older MBP's (perhaps even the new ones? Can we know now with the info that has been posted on other threads?) is just a Draft and was originally not even supposed to end up on the market.
There is no difference between Draft version 1 and 2, the only thing is that the 802.11 draft 2 will avoid people to buy products which in a years time (normally) will be THEORETICALLY useless.
I'm sure though that Apple won't do this to their consumers.