a good number of people here seem to be under the impression that:
1. hats NEED to be purchased and are unobtainable without spending money (other than the "upgrade from F2P thing", that's just basically buying the game)
2. hats are REQUIRED for gameplay (they aren't)
or some combination of the two.
so here are the facts:
Q. Why hats?
A. Why not hats? Valve originally added hats for whatever reason, they caught on, people started making their own, and Valve started putting the user-created stuff in the actual game. and since the Mannconomy Update, said creators are actually making money for their talents in 3D Modeling and such.
Q. Why are hats so expensive?
A. Because they're quite rare and quite difficult to obtain without spending any money. There are people who have owned TF2 for 2 years who haven't gotten a single hat drop. I got TF2 in the Summer of 2010 and have had 4 hats drop for me since. But this is true of ANYTHING, in games or real life. if something is rare, it becomes valuble.
Q. Why do people like hats?
A. For the same reason some people don't like hats; asthetic reasons. I for one love my Heavy Weapons Guy kitted out in a Blues Brothers ensamble of shades and a fedora (complete with a tiny Medic doll in his front pocket), since I think it looks more interesting than the stock HWG design. there may be those who disagree, but it's just like picking out clothes; everyone has different things that they think look good.
Q. Why are hats so sought after?
A. Aside from being unique and rare, hats are, at the heart of it, a purely asthetic thing. Just like a Shiny Pokemon. does it do anything extra? no. does it help you in any way? no. but do you want one? if you've ever played a Pokemon game from G/S up, the answer is yes. hats are many things. like a gemstone, they can be a fasion statement, a status symbol, a free load of cash, or just something someone likes. but like a gemstone, they also don't have any real purpose except to look nice.
in the end:
HATS
neccesary?
not really.
fun?
that depends on your opinion, but I'd say yes.