When you have a business, its far easier to just purchase a new machine and expense it than it is to upgrade existing machines. Time is far more value than money, and I'd much rather spend 3K for a new machine than waste a day or a week struggling with an upgrade issue and dealing with AppleCare.

PS: it's eligible for section 179 accelerated depreciation and sales-tax free in NY thanks to ST 121.3

Please note my reply was meant to be taken as a joke. I expect most people don't need to refresh their Apple gear on a yearly basis, but that is a bit of the stereotype of an enthusiastic Apple fan, and your post can be taken humorously to fit that image. Of course with Apple the answer is always more hardware. :-)