@Bass: When there is no difference between "The user asked you to quit" and "I've decided to kill you", the application has no choice but to behave properly and, when there is a known time limit, promptly. Because failing to do so means the app never exits cleanly and soon becomes an ex-app as far as users are concerned. It's different, albeit subtly, to applications being written with an assumption that they can take 20 mins to shut down if they feel like it (and if they aren't given that time, it's the user's fault for having forceful kill them)
And nobody said anything about killing applications as an alternative to VM. Windows 8 doesn't even do that, it'll happily suspend apps and shove their entire working set to VM if it can do that rather than actually kill something. It still has the ability to kill a suspended app if it wants to though and can do so knowing that app will cope (because for all it knew the last "suspend" was it being closed). This is a massive benefit when it comes to trying to service the OS, for example, because the problem of getting the end user back to "where they were" just goes away.
As for whether people enjoy the experience of working from swap, I'll just point out that, once again, the ability to manage resources so that the end user doesn't experience that, regardless of how many applications they have open, is a perfectly good metric for how good an OS actually is. The minute the OS actually starts forcing you to close applications (and decide which ones will be most effective to close) in order that it can manage resource effectively, you have a crap OS.