Whenever you buy a copy of say, Quake III: Arena or RtCW, you are generally supporting id Software to deliver more quality titles such as the above, in the future, just to use as an example. In the end however, they really are getting nothing, after all the money spent on ads, licensing game engines, PR team, etc. As long as it's something of high caliber, then of course I would buy them. More of a fickle opinion with me here.
M$ however, is self explanatory, as noted by other members.
Yes, when i had Windows XP, everything microsoft was... well Office XP Pro Costs $600 US!!! Whey the hell should i have to pay that kinda money for an office suite i can get free anyway for Linux (OpenOffice.org 1.0) that is comprable to office xp. I guess you get my point..