If you need to connect to a domain infrastructure, you won't be buying a home edition of Windows - or any version of Mac OS X - in the first place, so the whole basis of your statement is null and void. You will directly buy a professional or enterprise edition, and companies usually buy those through a volume license contract at 'slightly' different prices than you will find on Amazon.
I think that is a very broad statement. I've worked in quite a few companies where the executives and developers would be on Windows, and the web design and marketing departments worked exclusively on Mac. It is very simple to inter-operate if set up correctly. And this was even before OSX. Back then NT server had a service that could mount shared HFS volumes, or you could go the 3rd party route and use a program like Dave (http://www.thursby.com/products/dave.html) which is still around today.
In the above cases, all filesharing, printsharing, and authentication was done through a flat NT Domain, and later through Active Directory.