I would say that the difference is that your frinds don't go home with their very own copies of your boardgame after they come over to play it.
If they're all my computers, no one is going home with anything... Granted not many people (and definitely not me) have enough personal computers for such a thing, but my point is that if I have 8 personal computers, and I buy software, I should be able to install it on all of them.
Thankfully Stardock doesn't use draconian measures to enforce these things, because I've had terrible experiences with software that tracks each install and won't let you install it again until you've disabled a previous one. An example was Macromedia Dreamweaver. My old laptop died on me, and when I tried to reinstall it on my new one it wouldn't let me, saying my licenses were all used up and I'd have to manually disable a previous one. Sorry, Macromedia, but that's easier said than done when your previous computer won't even start up. 5 hours on the phone failed to get me anywhere, and I never bought anything from them again. A similar thing happened to me with MatLab, the only difference being that it took me an hour to convince Mathworks that I wasn't trying to steal their software and they reset it for me...
I don't pirate software, I have purchased every piece of software installed on my computers, except of course for freeware and the like. But when I'm treated like a thief by people whose products I have legitimately purchased, it sorely tempts me. If they're going to treat me like a thief whether I pay them or not, why bother paying them in the first place? So long as I have no plans to use software for profit, then I feel violated whenever a software-maker makes assumptions about me and my lifestyle.