You may think this is a small market, but more and more people are becoming hearing-impaired, and at increasingly younger ages.
As a hearing-impaired person (since birth), if all you have are uncaptioned videos with little text (and often NO text), I'll just be moving right along, your website is useless (to me).
Update: Just to be clear: For tutoring videos, I spend my money based on what's captioned. There are plenty of online video training sites: codeschool.com, treehouse.com, lynda.com, etc. I pay for the ones that are captioned, and look longingly at the ones that are not, as some of them look quite good otherwise. Ditto for streaming video - Amazon doesn't support captioning, Netflix (finally!) does.