Do you have a 3GS or an iPod touch 3G? Because in the 128 MB devices, Safari flushes the web page cache more regularly than you're implying. But when someone decides to wrap their own iPhone OS webkit browser, I think they have control of the page cache.

And just as an FYI, the iPhone OS SDK is open for both high-level (run loops) and low-level multi-threading (manual synchronization), so if someone wanted to create a Kitchen Sink for themselves, they could multi-task without jailbreaking. But what alot of work for something that Apple could make optional for the owner of the device. Maybe even let the owner decide what's multi-tasking friendly on a per app basis. I'm dreaming of course, because Apple hates me for my freedom.