With the MBA 2011 the connector sits very low such that simply putting the laptop down on a couch will disconnect the connector in my experience. It's the #1 issue I've had while trying to use an MBA.
If using a thinner connector let Apple fix that problem, that would be quite nice. Of course it's possible that it didn't. I haven't had a chance to try the new thing.
I noticed that, too -- adding a snap-on case to the Air solves that, at the expense of making it slightly thicker. However, I strongly prefer the texture/grippiness of the case, and it protects the laptop from a lot of damage (I still use a sleevecase, but I've had the laptop fall ~3m, cracking the plastic case, and otherwise fine). The cases have little feet on them, too, which raises it up to protect the connectors.
If using a thinner connector let Apple fix that problem, that would be quite nice. Of course it's possible that it didn't. I haven't had a chance to try the new thing.