In lines of code, the open source stuff (barring AOSP and Chromium) are a drop in the bucket compared to internal projects.
Also the easiest way for a Googler to open source a hobby project is to open source it under Google's repos - otherwise you need copyright assignments and stuff that's harder to get approved. So it doesn't represent what most Googlers work on.
The outside world, though, appears to have embraced it.