Here's the breakdown
NikeID has been around for a number of years, but previously the interface was slow, inconsistent, slow, and didn't work well on Macs.
NikeID as it exists today is super nice, all in flash, and runs super fast on my Mac.
I'm guessing Nike is now using Apple technology for NikeID, whether for creation of the site or the server backend. That's why there is the tie-in.
And for those of you saying Nike is dead, dream on. Not only am I a Mac-Head, I'm a Shoe-Head. I've got over 30 pairs, most of them over $50, and I quite enjoy them. There is a pretty significant subculture devoted to collecting shoes, both vintage, new, retro, and limited. They're the ones who camped out at NikeTown NYC overnight in the cold and rain for a chance to buy limited shoes designed by Pharrell, ESPO, and Jennifer Garner. They're the ones who waited in line for over a mile in Tokyo for a chance to buy 1 out of the 200 pairs of super limited Nike Dunks (the most sought-after shoes). They're also the ones who have significant money to spend, who follow closely what the "hipsters" are doing, and who are naturaly drawn to Macs and iPods.
Nike is cool because you can't buy certain styles everywhere and have a different ethos than other brands
Apple is cool because they focus on what others don't, and realize there is an intangible benefit to the design aesthetic of a piece of technology.
The more Apple can be seen as unique and interesting and worth-while by yet another segment of the population, especially younger people who are having less and less exposure to Macs in schools, the better chance Apple has to get new customers and make money. Which is, lest we forget, the aim of any business.