@MatthewDrury Thanks. I'm glad I'm not overlooking anything obvious, at least.

@Kodiologist Thanks for your comment - where I live it's illegal under anti-discrimination legislation for local authorities etc to publish images or video on their websites without alt text/a transcript that can be read by a screen reader.

But commercial websites don't seem to go to the same lengths. I do know Wikipedia makes an effort for alt text for images.

@Kodiologist, no you weren't being unreasonable. You were right.