I'm not sure this is fair. Google is a large company with a lot of products. You simply can't expect top management to be an active user of all of them. I'm sure Apple doesn't require its top execs to own an iPhone, iPod, iPod nano, iPod touch, iMac, MacBook Air.... you get the idea. The comparison with Twitter is even worse. Twitter really only has one product.

The way this data is organized, I don't see any top executives not using Google+ that "should" be using it.