I think it would be naive to imagine that this is a move based solely on ethics (but, then, you never know - I wouldn't want to do them the disservice of ruling it out utterly).
But to do it with such direct criticism of the Chinese government. Even if it is a veiled reference there can be little doubt about the claims. The only inference I can think of is that they are very sure (or have proof) it is the Chinese government that are responsible (I cant help feeling if it was corporate or extremist groups etc. they would be directly named - or at least more clearly referenced). It's a huge political statement.
Im glade I stuck with Google through the last few months and the spate of anti-google sentiment starting to emerge (the cynic might suggest this grand gesture is related...?).