Google is currently being investigated on anti-trust issues . A huge show of political force might annoy politicians. Google's just being careful.
"might annoy politicians"
That is the whole reason of protesting. Any law would pass if they can't be bothered.
How about the current adsense campaign? That looks like a very large political show if you ask me.
I think the blank out of Google is making more of a point then say if they blacked out Gmail or Youtube.
Blanking Google mail would harm the user base. I support doing so for non-essential services but many of us require access to our mail accounts for a plethora of reasons.