Gmail, Docs, and News are not dominant in their category, Images is just another form of search, while Reader is dominant but increasingly irrelevant.

You forgot Android, which in the long run will probably prove to be their only really big hit other than search, at least that they've released so far. The others just don't matter that much.

Android is also an acquisition, FWIW.

What about YouTube? It's much more successful than the last 6 of your examples (maybe except Maps)

YouTube was an acquisition.