I guess you've never seen the "I'm a Mac, I'm a PC" advertisements. I don't think the consumers produced them. You've got to take into consideration that a company is always looking at the bottom line, and if it's in their best interest to sell something on a competitors systems, they will do it because it make good business sense.
Of course I've seen those, and they are but friendly competition.
Those commercials, in no way, convey the sense that Apple and Microsoft
hate each other -- but they do convey the sense that the two companies are in competition with each other, and that one company thinks they have an advantage, or a better product, than the other.
It is quite possible to compete with a company without hating or wishing ill will on another company. In other words, "animosity-free competition," which is exactly what Apple and Microsoft had for the large majority of their relationship.
The reason Microsoft Office came to the Mac was more than just Microsoft wanting to make a financial gain. Part of the deal was because the Mac was, indeed, and like you say, a viable market opportunity. The other part is because Microsoft was "bailing out" Apple, and part of that deal was that Microsoft would commit to supporting Office, IE, and some development tools on the Mac. Read about it:
http://news.cnet.com/2100-1001-202143.html
If all Microsoft was concerned about was money, Occam's Razor dictates that they would
not release Office for Mac, that they would
not "bail out" Apple, and that they would let Apple go out of business (which was a LOT closer than a lot of people realize -- Apple was, indeed, "running on fumes" and going downhill FAST), giving people
less choice in the marketplace. People who would have otherwise purchased a Mac would now be forced to have a single choice: Windows, giving Microsoft
tons more revenue than selling a single copy of Office to a Mac owner.