On my server, thorium prices aren’t any where near what you guys have. In fact, the best ore for profit per danger involved per number of veins available is something else lower than thorium.
Another reason for higher prices is just that more money can be made by higher level characters, so they’ll buy things at higher prices now. Prior to TBC, I think most people were averaging about 20g an hour on straight up farming, assuming no drops that you would later sell for more money (thus skewing your per hour rate because you wont necessarily do that every hour). Now, it’s at least closer to 40g an hour or possibly more, if you have some ‘top secret’ location, and not just for a level 70 char. Due to the prices of raw mats, a trade skill may be able to net you even more than that if you choose not to do straight-farming.
Stealth-mining by a druid or rogue has always been a good reason to do it on that class, even if you’re around the same level. Not having to fight everything except the mob close to the ore vein you want works very nicely.