What is it about TF2 and hats?

I see in a lot of posts talk about Team Fortress 2 and hats, what is that about?

What is so special about hats in that game?

The TF2 Forum community has had a thing for hats ever since the Spy / Sniper update when they (and the random drop system) were implemented.

They like to complain about hats, cheer about how awesome their hat is, or worry that too many people are complaining or cheering about hats.

Of course, it may have all petered out, but Valve decided to add more hats. The classless update only added fuel to the fire with such quotes (from the Blog Update news itself) as: http://www.teamfortress.com/classless/day01.php or,

Throughout history, men have worn hats as a way of showing how much better they are than other men. “I buy hats,” a behatted man seems to say. “I am better than you.”

It appeared to reach its height when the Valve blog (not an update post, mind) itself seemed to indicate that hats were the most important things to the developers.

Observe.

Suffice it to say that Team Fortress 2 is no longer a first person shooter with RPG elements. It is 100% a hat simulator.

This comic more or less explains it: