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.
However, the author of the article mentioned that Google is saying Google+ is THE future of the company. In that case, everyone should be using it. It's not "just another" product.
The author cites this article, which (ignoring the fact that it is an interview with Google ex-CEO) doesn't even mention Google Plus by name. Personally, I'd say that the author's post demonstrates that Google doesn't think Google Plus is central to the company's future.
Yeah, 'cause it's not like the current CEO has tied every employee's bonus to Google's success in social, regardless of whether or not they work on the product...
It's completely fair. It's one thing to simply not use a product (Google+), it's entirely different to actively use a competitors product (Blackberry). I bet there would be hell to pay if Apple execs were walking around using Blackberries and Win Phone 7's.
The way this data is organized, I don't see any top executives not using Google+ that "should" be using it.