I've seen a (reasonably big) company that has deployed a Citrix VDI cluster exactly for this purpose - for MacOSX/Linux users to deal with both of problems you have listed, plus a third one:
* Legacy Intranet websites that only work in IE.
* Legacy Intranet websites that only work in IE.
The person I'm talking about is self-employed and not, erm, technologically affine, so why not just stick with Windows?
> why not just stick with Windows?
Hm... because Windows is essentially a platform for Microsoft and assorted 3rd parties (most of which are not even affiliated with them) to spy on and meddle with you beyond any reasonable control or limitations?