This isn't how Apple would likely introduce change*. Right or wrong, they tend to be more focused. Plus as mentioned by others, Apple has other products for most of those requirements and I think the commentary has been pretty clear Jobs was unlikely to consider OS X an acceptable tablet interface (plus those Windows 'successes' of the last seven years). Maybe Android/Chrome OS (which should be part of this larger discussion), may (likely?) go down a hybrid path, but Apple doesn't 'slap' anything on.
I really think the Flash discussion needs to be on the side (and again pulls Google, etc. in), and as mentioned by others, multitasking is likely to be introduced in the next OS update (though if controlled threading, etc. is part of that we'll see - stability is rising in importance and limited multitasking has always been part of the OS).
Way I see it, as soon as you decide on a Linux desktop environment, compromises are made, and that's long before the more restrictive Windows or OS X most users accept. We all laugh at the not far past of hunting down video drivers for every application or avoiding laptops because their hardware isn't 'open.' This is just the next step... for some/most.
* Then Intel move is the only recent I'd consider gradual and that was only an internal shift.
Also: northtemple - On iPads, Grandmas and Game-changing