How in the hell are they gonna add in a vendor search when they don't even know how to fix the character & guild searches!?
Because those two things are probably dictated by EA corporate security polices since they involve accessing in-game data through external websites.
After all of the security problems that other companies had (Sony PSN LOL), and even later after BioWare's major security problems with one of their official websites
Updated June 23: Important Information for BioWare & EA Account Holders that exposed "user names, encrypted passwords, email addresses, mailing addresses, names, phone numbers, CD keys and birth dates", EA security seemed to have gotten a bit panicky about what games and systems can push data to the web. EA was already panicky after watching Sony catch **** left and right over its problems.
That's not to say that the person(s) who would/could work on an in-game vendor search could also work on external character and guild searches, they probably would be the same person(s), but EA is extremely touchy these days about things that touch internal data.
I really question whether the Mythic MMORPGs will ever have their full web functionality restored, or at least anytime soon. Newer games that have that stuff, like SWTOR, were able to have a lot of work done on their systems from the beginning.
For Warhammer, Camelot, and UO, there probably has to be some changes with their databases, or somebody has to do an audit and then clear it, and they are probably low in priority.