Going on sales figures - I'd argue that's no longer the case. People want smartphones and Android is cheaper which is probably a large reason as to why it's done so well, though I'd now say Android and it's app store is getting a convincing enough option on it's own right.
My opinion of the best phone ever is one that is always up to date and can access all the features of the most up to date version of the OS, hardware permitting (ie, I wouldn't expect my Desire S to be NFC compatible). I'd personally say that a dual core 28nm phone with a 3.9" screen, 128GB of storage + SD Card, removable 2,500mwh battery and an aluminium unibody is the way forward, however, that is not what I would sell.
I'd sell a "superphone" with a 4.3" screen with epic specs and a standard phone with a 3.7" screen and high mid-range specs to start off with.
I think that a phone that's always up to date (software wise) would appeal to many. Ask an iPhone 4 user if they're pissed they can't use Siri just because Apple say so, or, for instance, a HTC Desire HD on Orange user if they're annoyed they've only just got 2.3.5 with Sense 3.0 when others have had it for
ages. Yeah, not everyone cares (my sister has a GS2 that still has it's default homescreens....
), but I think that the promise of always up-to-date and very customisable OS would be a really good USP for an Android device.