I think Flash would still outnumber WebKit. Flash is bundled with the Chrome browser, many (all?) Android devices, the RIM PlayBook (but not BlackBerries, AFAIK), webOS phones and tablet. Mac OS X used to bundle Flash, but new Macs do not. Windows has bundled Flash for a long time; I'm not sure if it still does.

For now, the number of Windows PCs worldwide is probably larger the the number of iOS devices, new Macs (if the user hasn't installed Flash to watch YouTube), and RIM BlackBerries. But Apple is selling a LOT of iOS devices, so the balance may shift.