It costs roughly $1 for a professor to prop his camera up at the back of a room and record himself speaking for an hour, then post it online (11GB @ 3¢/GB = 33¢; we'll add double that for bandwidth &c.); it costs $180-$600 to close-caption that video. The ADA turns lecture videos from something anyone can do to something basically no-one will do.
Yes, life sucks when one's deaf. Yes, it'd be awesome for every organisation to have the resources to close-caption every recorded lecture. But requiring every recorded lecture to be close-captioned merely ensures that to a first order of approximation no lecture will be close-captioned.