Exactly.
Even though you can have several users logged on, it doesn't mean they're actually using the operating system at the same time. This is only possible by using several monitors, keyboards, and mouses in which case each user would require a separate licence.
I think this is stupid, whatever happend to fair use?
Providing you're not using the software commercially you should be able to install it on as many machines as you like providing it's only for personal use.