I don't understand why they're taking that decision away from me. They could just enable auto update by default so most users would always be up-to-date unless they have a reason for disabling it. There are some good reasons other than money as well, such as privacy and security. I don't want my computer updated in any shape or form when I'm on an airport or in an authoritarian country for instance.
I don't know whether a Chrome update is dwarfed by regular browsing. The link you posted shows the size of one particular diff update they did. That's a completely worthless measure. The worst case, no doubt, is that everything has to be replaced and that would be 10MB.
Security-wise I'd be very surprised if Chrome updates weren't signed; MITMing of auto-updates isn't exactly new (see EvilGrade). So I doubt it's an issue there.
That said, I agree that there should be an option (not a prominent one) to switch it off.
(But I also agree that should be your decision to make.)
The compression Chrome uses on the diffs is pretty hardcore:
http://www.chromium.org/developers/design-documents/software...
So you can at least be reasonably certain that your browsing bandwidth dwarfs the Chrome updates, FWIW.