I've seen some registration pages that have a "skill testing question" in addition to having a captcha. These skill testing questions are usually easy trivia, such as "what is 2 + 2" or "who invented the light bulb?". Registration will not go through unless the correct answer is given. What is the reason behind having such questions? If a bot already got past the captcha, there never seems to be a large pool of questions so the answers could be hard coded in. If a human in a 3rd world country is getting past the captchas (which to my understanding is why they don't work well) they could also solve a skill testing question (provide they have access to a search engine).
Bots are usually made generic. There is no bot to register specifically at Celeritas.domain and post spam. There is a bot to register at any generic Wordpress/xForum/yCMS site and post spam.
It is very hard to generically write a bot that can answer "What is one plus -2", "What color is a Firetruck?", "What is the name of this Blog?" and whatever else such registration questions can be. Posting spam on a single website is (currently) not valuable enough for this Spammers to pay humans to solve this things.
If there is a new Captcha system used at many domains, it is worth the effort to implement that. For a single site, the effort just isn't worth it, it seems, even if the effort is very low.