Numbers alone must not be the driving factor for technology decisions. Both mainstream (80/20) and edge-case requirements must be addressed, because for online information, there is:
- No standardized user, and
- No standardized device (browser or other user agent) for accessing information.
Longdesc usage is not and will never be widespread because:
- People with disabilities are a minority.
- Images that need longdesc are a minority.
Some commentors have suggested that in order to sustain a small language there have to be some screening factors, and frequency of use in the as-is Web is the screening factor to use.
The WAI position on this is roughly "that is like saying that the builder of a high-rise building should decide whether or not to include fire-stairs based on whether the previous buildings at that street address had burned down or not."
We don't build fire stairs just enough to evacuate 80% of the occupants.
Accessibility features address failure modes that are infrequent, but critical when they occur.
Popularity among authors should be used to select between _functionally complete_ alternative strategies for supporting required functionality.