Until someone can definitively show me that the OS has an impact on the end result of the program (e.g., 2+2 =5, or that an image renders differently because of the OS and not LR/PS), then the decision becomes one of personal preference. I pretty much agree with Jeff, that we've beaten this poor horse into submission.
If only it was that simple.
Pretty much every car will get you to your destination, yet there are difference in how much cargo you can carry, reliability and comfort. Some of the factors are personal preference and some are monetary.
Let's look at something closer to topic. If I save a photo to a hard drive, I will read back the same bits whether that hard drive is a simple consumer disk, or a fancy hardware RIAD. Even though I get the same results, the RAID has advantages (increased reliability & speed) over the vanilla disk (which costs less). The choice of consumer disk vs. RAID is not simply a personal preference choice, there are business consequences (for some the reliability of the RAID justifies the increased cost).
When it comes to Mac vs. Windows, Photoshop and Epson will both give you the same results today.
For some of us, we are also concerned with the costs to maintain the system (repair failed hardware, fix corrupt software, etc.). Some of us don't have the resources to dedicate a machine to Photoshop and printing, and would like to use the machine for other purposes as well. A machine that can run new software as well as old software has advantages in situations where resources are limited and flexibility is needed.
I'm not trying to tell people which platform to use, I'm not trying to tell people which platform is best. I'm just trying to have a rational discussion about one of the differences between Apple's and MicroSoft's policies. Knowing these differences helps people make informed decisions.
Saying the only difference between Mac and Windows is "personal preference" is clearly wrong. There are many differences, some of which don't matter and some of which do.
Trying to justify the differences may be interesting, but irrelevant. If Apple abandons legacy software and MicroSoft doesn't, the difference itself is far more important than the reasons why.