MS never forced anybody to buy anything, but they did give them attractive choices, such as:
You can pay $40 for every copy of windows you buy from us, or you can agree to buy one copy for every system you make and pay us $20 each. Nobody was forced to choose the latter, but that choice was usually the best one. Try to buy both a Pepsi and a Coke at your favorite restaurant if you think this kind of marketing is restricted to a single company or industry.
As far adding stuff to the OS goes. MS operates just like every other manufacturer. Microsoft wants you to buy Windows 2005 and Windows 2007, etc. etc... The best way to get this to happen is to add stuff to Windows that people want. Things, like disk compression tools, backup tools, CD-writing software, browsers etc... that people seem to be willing to pay a small amount for are obvious additions to something like Windows. Also, Ford puts stereos in their cars, and people who want to sell you an add-on stereo need to produce one that is of sufficiently better quality that you are willing to spend money for it. The same holds true for software products, if somebody wants to sell you something (say Windows or Netscape) that you can get for free elsewhere (like Linux or IE), they need to make it attractive enough that you are willing to spend the money.
Windows has added tons of features added in the last 8 years (see list above) that were only available as add-on products previously. Giving free stuff to consumers does not harm them.
Hooligan