The Twitter/Facebook icons are large to promote clicks. Social media is the easiest and best way to stay connected with a userbase and until now, our attempts to crack Facebook have been... lackluster, at best. We're slowly working to change that. Large icons to help sway users to follow/like us is just one step toward that goal without cluttering the page with a Facebook feed (which I generally despise on sites).
I still need to work on the IE10 problem with the avatar opacity. I would have done it already but like I mentioned earlier, I don't have a copy of IE10 for testing yet. When I procure a laptop that will run it, I will make the change. Overall, the design on those is still somewhat up in the air. I'm not tied to the existing design but I have other priorities right now that push that particular element to the background.
If you pick up a 7" tablet, you'll see why the current design trend is toward larger fonts.
While you may be an advanced enough user to operate the zoom feature, as a designer I cannot assume that is the case with the vast majority of users (after all, 9% of our users are still clicking away under IE8, the worst browser with significant marketshare). I have to design for stock configurations as much as possible with the assumption that the average user will do nothing to make a site more or less readable in their browser settings.
One year ago, our tablet traffic was 2-3%. Right now, it's a little over 10%. By the end of the year, I expect it to be 15% or better. And over 50% of tablets sold today are 8" or smaller while the biggest tablet sold in any quantity is just 10.6". A full 25% of our traffic now comes from tablets and phones. By this time next year, I expect that to be 33%. It's the fastest growing segment of the internet and those form factors have to go into any modern site design.