That's what I thought it was, there are a couple ways to do things when it comes to resolution. You can either just let it do whatever it wants (which means things might not look right), force it to take one size and put a colored background around it (which seems to be what is going on here), or as you stated. The second solution is generally viewed as the best, but has to be tested at various resolutions to make sure that it doesn't do what is being done here (in my case I have just a little grey on either side, it all looks fine).
Not sure what happened to change it, but this should be enough information for the web guys to look into it and get it fixed.
If anyone else wants to post their experience, try to include OS, Browser (and version, if you know), and what resolution your screen is set at currently.