Browsers: Rounding Error?

Microsoft's Ballmer recently described the share of competing browsers from Apple and Google as a "rounding error". While Microsoft's efforts have left it significant desktop browser share even after its recent declines (the halycon days of 95% share are long dead), the share of browsers in the mobile space offers an entirely different story:

Source: PC World (direct link here)

The version of this image that shows up here misses a comparison pie-chart with different numbers, so click the link. The fact that different measurement methods yield such wildly divergent results is certainly interesting (Safari's share is 36% ... or 66%?), but the most interesting thing is that share for WebKit browsers (Safari, Palm's Pre, Google's Android/Chrome, RIMM's Blackberry, Nokia's Symbian S60; more discussion here) seems to be taking over the world in mobile browsers just as predicted. Aside from Opera, which has a significant installed base, is there a serious competitor for mobile browser engine share? It seems a bit like the original America's cup in 1851. You know:

Queen: And who is second?
Attendant: Your majesty, there is no second.
-- interview with Stuart Alexander (alternate version recounted here)

Microsoft may have committed to delivering quality products in the future, but at least with WebKit it's the case that the rest of the world is already delivering. With Windows Mobile an apparent marketplace failure in the segment of phones capable of delivering a usable browsing experience (and WinMo suffering non-Microsoft browser competition), and mobile devices exploding at a rate not seen this century in desktops, it seems WebKit's star is on the rise. Meanwhile, Firefox gains steadily against Internet Explorer in the desktop space.

Who's got the rounding error?

UPDATE: while the browser's rendering engine gets top billing -- people think of browsers and expect to see HTML rendered -- there are other important components to consider, like the browser's Javascript engine. Although Apple's Squirrelfish Extreme looked like the field leader around the time of Chrome's launch, Google's V8 javascript engine has matured to take the top spot. Sadly, Chrome isn't available on any Unixlike operating system yet, except for the especially adventurous. Anyone with Javascript performance benchmarks more recent than January are welcomed to post :-)