With the exception of certain esoteric applications and managed packages, that's absurd. All the Windows software I bought has no support terms dealing with the OEM. Do you have software that says "Support only valid if you run it on a Dell, Gateway, HP, ....."? Apple is just another OEM when it comes to Windows. And VMWare for the Mac is like running VMWare on Windows or Linux. It's not a problem specific to the Mac.
It’s a matter of testing effort and being able to repro problems. Apple is vastly different hardware, which opens it up to vastly different problems, and every company has to decide where to spend the money to build expertise. Dells, Gateways, and HPs are all still basically the same machine, Intel based PCs with CPUs from the 8088/86 line. For a while nobody supported AMD CPUs, not necessarily because there was anything wrong with them but because nobody was convinced their product wouldn’t have unique problems on AMDs and the market share wasn’t enough for them to justify the testing effort to verify it. I never said VMWare on a mac was any different, I said there were differences between running under VM and running in a real machine which causes some companies, including the one I work for, to limit our support of it.