What you describe is exactly what Jobs said when he introduced the standard dock. There is a button on the home screen that starts a slideshow.
Regarding multitasking (without getting into Computer Science too far), there are two kinds. The first is when something needs to keep going while you do something else. In that case, the ‘system decides’ how to parcel out time from the processor. The iPad is (currently) very stingy about that to conserve battery charge. I expect a very clever way of dealing with this in the near future.
The second, and often more important, is the ‘user decides’ to do something else and come back - like switching to a different browser tab. This is supported by the iPhone/iPod/iPad browser, but not with tabs, with ‘pages’. A variant on this is to switch to a different ‘app’, which as noted can be done by preserving state and switching. IIRC, this switching technique was common 20 years ago before true multitasking OSes appeared for PCs. It was clunky because of slow memory access, but that no longer applies.