There's nothing you can throw at a MBA that won't run. It's whether or not it will run well. For example, I wouldn't want to try raiding in WoW, on a low end 11" Air. That doesn't mean I can't, but that it's not recommended. Similarly, app developers would be better off getting a MBP, as it has a much faster CPU. Obviously xcode will run, but will it run well?
Just because you can run Word without trouble doesn't mean the MBA can do everything well.