Do you not loot the sparkly things when they die? O.o I don't mean to be rude but really I don't see how people aren't carrying at least 2-10k as pocket change these days.
Most people that make a lot of money either just do things that generate decent money and rarely anything else, like every single daily, or work the auction house in some form like duel gatherers or auction heroes.
I am not exactly poor, I have around 60k between all my characters, but I am picky about what I use it on since it covers more stuff. Do I want to put a whole set of green gear for that alt that I will only use for two levels, or do I want to buy that Scorpion Mount, or those really expensive jewel-crafting mounts, or maybe that 100k Yak. Do I want to hit the AH and blow 5000g on that epic bracer that I would likely upgrade with VP or LFR? Or do I want to hit the pet store and buy pets to complete my collection?
With JP, I don't have to make that choice. I get both currency from running dungeons, so I save one for my gear and the other for my "extras".
JP have a place and I assure you that if they ever didn't have a place Blizz could just add in something that uses them. I saw someone mention xmog earlier that would be pretty cool to use them to buy old school gear. I personally run out of things to use JP on for myself but I can always buy some mats from the trade vendor and make bags for the guild.