Most software now, it wasn't like that not too long ago. Yes, you can get an OSX license for 5 computers for $200, Vista is $300 for one computer which cannot be transferred and has a limited number of activations. The main difference between Vista and XP is not only the EULA, haven't you been following this thread? Vista incorporates an embedded layer of DRM which cannot be disabled as well as a much more restrictive activation system.
Not now. Most softwares, maybe ten years ago, are supposed to be used on a single computer.
And this thread is about the "one transfer" rule stated in the Vista EULA. DRM or other things are not relevant. About the activation system, Microsoft actually said it will be less restrictive (you can change more hardwares before the need of reactivation).
The vast majority of software cost is in development (and a minor amount in computer hardware as well as other software which is also typically overpriced) and please, most companies rarely if ever modify their software to any significant extent except for some specialty uses, most is security patches and minor updates. Of course they make new versions which they then charge full price for and often require for new file types. Once the software is done and revenue exceeds dev costs it's all profit. Unlike hardware which requires constant costs for the machinery, labor and materials and which cannot be reproduced easily, software can.
Do you think a software developer can write a software, sell it, and just wait for money?
The reality is, most softwares need modifications throughout its history. And it's not just about security patches. Whether the modification is for special uses or not is not important, because it still need manpower to modify the software, no matter how many people need the modification.
Even Microsoft can't sell the same thing over and over, although many people seem to think it's the case. Not to mention the security patches, Microsoft still have to cope with new hardwares, fix issues with certain softwares, etc. These all cost money. Support cost is also significant. What happens if a customer complains that Windows XP doesn't work on a computer? You need people and time to find out what happens, and sometimes you need more people and time to fix the problem. If support is not an issue, why did Microsoft have to end support for Windows 95/98, and there are people actually complaining about the end of support?
Hardwares are quite the same as softwares. Although many people tend to think the cost of a hardware is the manufacturing cost, it's not just that simple. Many hardware products have quite a lot revisions over its lifetime. Some revisions are to reduce cost, others to fix problems, or to increase stability. These cost can also be significant.