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  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.
 Including all
the canon we're going to get after tonight, until Season Two. At least, according to the PTB. Waaaah!