Google has so many products, how would you expect a typical, hard-working employee to actively use all of them? They just wouldn't get any work done.

When their bonus is tied to the success of the company in social software, you'd expect them to use it. No? If Google is trying to make an identity play, shouldn't identity start at home?

Most people make enough money to not need a bonus, so they might value spending their time not caring about Google+. I could make a lot more money as a hitman than as a programmer, but for some reason I choose programming.

Steve Yegg doesn't use Twitter either.

If he was someone who was active on Twitter then yes, you'd have point. Otherwise...