I don't know if MediaWiki has any sort of "trusted domain" feature that lets you avoid captchas for certain domains. Even if it did, though, much [1] of the canon content comes from the character LiveJournals, and adding "livejournal.com" to a trusted domains list would open up the wiki to a lot of spam. Yes, the captchas are annoying, but you get used to them after a while, and a bit of annoyance is better than having spambots infest the wiki.
Besides, the word choices are sometimes ... amusing.
[1] Including
all the canon we're going to get after tonight, until Season Two. At least, according to the PTB. Waaaah!
