I'm an engineer with a pretty keen eye for design, but I've never understood these font wars. At a certain point, whether your serif is 3% longer, or the loop in the letter a is downwards or upwards, none of that helps or hurts readability. What companies really need to start working on is their rendering technology. The Segoe family was designed for clear type, one of the most readable and cross-screen technologies available today. Mac OSX suffers horribly from a blurriness on non-Apple displays, and as unfamiliar as I am with the tech that underlies Linux distros like Ubuntu, they haven't seem to hit any screen right yet. ClearType handles bleed, leakage, contrasts, all seamlessly. Apple has only designed for their devices, so yes, it tends to look very good on their tech. Android gets the worst of both worlds: no good algorithm, and no control of hardware.
Roboto may be clumsy, but it's far from a patchwork of existing pieces. (if you look, really look, at those comparison charts, you'll notice that even the "frankensteined" source fonts have significant differences from the Roboto glyphs they inspired, in weight, shape, and proportion. the bar on the capital Q looks nothing alike, for the most blatant example.)
it's not the case that Roboto is a ripoff of an existing face, or even four existing faces (for the special case of "an existing face" == Helvetica, I posted about this at length here at my blog, complete with ranting and bad photoshops: http://http204.wordpress.com/2011/10/19/all-sans-serifs-are-...). it is the case that it's a product of its times and took inspiration from faces which already existed -- because if you create a font from scratch, intentionally trying to do only things which have never been done before, you're likely to end up with something completely unreadable.
that said, to me, it's super unrefined, chunky, and challenging to read -- it's outright broken at small sizes (and, thus, on low-DPI displays) where letters blob out around the edges due to poor hinting.
I'd much rather they just bring back Droid Sans. :(