From what I read here is that they send a WM_CLOSE equivalent to the app, which has an undetermined (yet) time to swap down. This means that it's a high-level function. In order to save or close, the OS has to multi-task, otherwise no timeslices for the bg app.

Also, from what I read, it's not that they don't multitask, it's just that they whitelist apps. That is, some apps that take little resources will have the feature, while massive apps will pause everything else to maintain performance, save for internet and audio (which still work).

It's not a bad idea. Plus, it's a checkbox somewhere. It's not like it's missing support so it kills the platform. The way I understand it, the "feature" is temporary until they can maintain a good user experience which is a priority for WM7, which suggests they plan on unlocking the beast during this version's lifespan.

Frankly, if I have audio, web, mail and a few others multi-task, plus services, it's not a killer. Plus, it's very, very likely it can be fixed 3rd party if MS becomes difficult.