It's not really support or economics that apple use to justify their decision, it's the fact that (in theory, cough, leopard upgrade) osX on mac hardware just works. Everything works fine out of the box and that user experience is priceless, even if they doubled their market share, if they lost that 'just works' impression it would be a disaster for them.
There's actually talk that the server version of leopard will have a EULA which permits virtualised installations of osX. The question will obviously be, virtualised on what? If it's VMWare I think thats a good deal and it'd be sensible to extend it to demo version of the desktop os. VMWare is useless for graphics and media so it's never going to canabalise sales but it shows people how the OS works (then again, how useful is that with a keyboard which doesn't have the apples keys.)