Google's extensive testing does not preclude the possibility that their design sucks. The original "simplicity" of their service was entirely accidental; if I'm not mistaken Sergei either didn't know enough html or didn't care enough to bother making it any more complicated.

Religiously testing will only lead to a local maximum and ignores the possibility that the design may have not been great to begin with.

Google's homepage is not even remotely close to the standard a highly competent minimalist designer would offer. Little attention to detail, remedial typographical choices, a 90's looking poorly executed Logo, random UI elements with no clear purpose. It's very much like an engineers interpretation of what a minimalist designer would do.. which is exactly what it is.

All of their products are on the utilitarian end of minimalist design and could stand to be improved significantly from an aesthetic perspective without actually changing the interface noticeably.