Its not really NEEDED per se, but easily gained. Tell me: If you were to go out into Talus Chute, and kill an enemy. He happens to drop a...Req 8 15^50 Summit Axe (worth about 200-250k), would you sell it for 10k to someone who most likely (upon realizing its actual worth) re-sell it for +100%'s of profit OR, try and attain that maximum profit for yourself? Well, if youre smart, you decide to sell it yourself, pocketing a nice chunk of change. What are you going to do with that? Any shiny new swords or axes at Drok's Mall or LA Department Store? How about that nice 15k armor up in Granite Citadel or Marhans Grotto Storefront Windows?
The point is: you can find a lot of things to spend your gold on. Perfect and Near-Perfect weapons are an avenue that many choose to pursue to spend their gold on. 15k or Fissure Armors are another avenue that many also choose. Even just maintaining your characters becomes a lil costly.
No, you don't need all that gold, and statistics show that ~75% of guild wars players have less than 20k on their accounts. But,
if you got it, why not spend it? I mean, what else are you going to do with it?