I can't see a way to define the limits of such an exemption without getting collateral damage, so maybe, this amount of collateral damage is about the best we can get?
Also, in the Berkeley case, part of the reason Berkeley deemed the costs too high was that Berkeley had a large backlog of such videos. They have been making new content accessible since spring 2015 (that content also is behind their firewall to prevent 'pirating' (http://news.berkeley.edu/2017/02/24/faq-on-legacy-public-cou...: "Pirates is a term used to describe websites that embed YouTube content without the permission of the original copyright holder for profit. UC Berkeley legacy Course Capture content has been discovered on for-profit websites, which use either a subscription fee or on-page advertising"; "UC Berkeley stopped posting course lecture videos publicly through webcast.berkeley.edu in 2015 as a way to reduce costs and increase adoption.")
Adding a wheelchair ramp is a small fraction of the total costs of making a building, just as making a website properly is a small fraction of making a website. So it's somewhat reasonable to require the (relatively small) change to make the thing more accessible.
On the other hand, in the Berkeley online classes situation, making the lectures deaf-friendly (i.e. doing transcripts or subtitles) was much, much more expensive than making the lectures available in the first place, which amounted pretty much to setting up some simple gear to record something that was already happening. In this case, the required costs were totally out of proportion, and meant that the content became less accessible, i.e. was taken down for everyone.
So the regulations must be taken with a grain of salt - it's easy to write (or interpret) a single sentence that makes a requirement totally disproportionate and not comparable to a wheelchair ramp.