1) iLife is the reason why mac sells! its the ready to use out of the box thing that attracts new mac users .. how can they offer the same on some other platform?
2) it wont prove to be good financialy either, because it will be just a matter of time before iLife 07' Windows Edition will flood the P2P, torrent and usenet networks ... no green paper for Apple.
3) iLife will just 'complete' windows, with the vista's security, microsoft's productivity, iLife's entertainment, massive PC gaming platform ... Apple will lose some serious market share .. (well this might not be all true to be honest, there are several other factors as well, but this will do)
4) the PC in mac ads will no longer be a fat ol'd bloke wearing brown suit, and that will be quite sad.