Doesn't matter what you have "open" I can open 30 tabs, word, excel, outlook, powerpoint, ichat, garageband, itunes, quicktime, photoshop and whatever else you want open and still have nearly idle CPU usage. All that does is increase your memory usage which is not going to generate heat. Do something that actually needs significant amount of CPU, or better yet, CPU and GPU usage and you WILL hear the fan loud and clear.
The folks complaining of fan noise aren't doing so because of their imagination. I own an MBA and have worked on about a half dozen other 13" MBA. Every single one, without exception was VERY audible when under load. I was skyping with my cousin who recently got an MBA and after a few minutes of video chat he said "dude, my laptop is about to take off" due to the ever increasing fan noise. This coming from a guy who built PCs using 6000RPM delta fans a few years back so he's pretty tolerant of noise.