VMware merely passes relevant host information to the guest.
For OS X this is something (can't remember) that satisfies the "Dont Steal Mac OS X" kext. For Windows and PCs with embedded license signature keys (again, can't remember the name, SLIC or something like that) then they're passing that (making virtualized Windows+Office OEM licenses activate against the original hardware†). VirtualBox does not (or did not last time I had to patch it), and it's a pain, putting you in all sorts of legal grey areas for something the license allows.
† also works on a hackintosh