its not so much that android needs dual core or others don't, in my experience as a pretty heavy phone user but by no means an app power user I genuinely don't think any phone needs it.
Android however does seem to be spinning a bit into the world of the PC spec race, 1ghz! no 1.2ghz! 1.2ghz dual core! 512mb ram! OMG I wouldn't have a phone with less than 1gb ram! Etc. When I think the chances are for the vast vast majority of users it makes precisely no difference at all. Just like it does with computers. I can only assume its specs and saturation by options android has to put up in a sensible fight with apple.
Unless I'm playing a game for which my PC is practically custom built and rarely used (a-la dual core mobile phone processors, gigantic screens etc) I don't notice any real perceivable difference between my desktop, laptop with a low voltage cpu, my old netbook with an atom or my mac mini with its core2 underpinnings.
The only specs I would ever consider buying a phone on are camera (although thats quite subjective too), weight, size, memory capacity (as in storage not ram) and battery life.
oh and maybe screen size and resolution, I get that people like that although to state a personal point of view I think past 4" gets unweildy for the majority of "phone" tasks. I watch tv on my tv funnily enough.
Having used the 800 there ws no lag or slowdown, in fact for transitions between menus and scrolling etc it had my SGS2 well and trully beaten.
The OS felt iOS-ish in its fluidity and intuitiveness. Thats not to say I find iOS flawless, its just much much better integrated for a good out of the box experience and thats what I'm expecting to get from both the N9 and 800 tbh.
I just hope nokia don't get drowned in the building mobile e-peen wars. Who cares what the hardware is on paper if it works?