It's provision of programming accessible to the deaf community. I think the expectation is that people will record the stuff they are interested in to watch in the day time so the sign language has to be available as standard rather than a "red button" option.
When it comes to why sign rather than subtitles I guess some of that will be individual preference and some will be to cater for those that can sign better than they can read English.
Can't, but you can read foreign books.lol.
Switched from a ABmobile (no related threads) & discovered signing isn't universal.
Someone said on thread about voice overs on TV for the blind that it was handy for their father who was deaf????
Sign languages do not follow an international standard.
For example, BSL (British Sign Language) is incomprehensible to a person who only knows ASL (American Sign Language), let alone the sign languages of other nationalities e.g. French, German, Dutch etc., etc.
My eldest sister is deaf and we used to watch programmes with sign language from quite early on long before subtitles appeared. All our family know how to sign language. Its very interesting and should be made more available for those wanting to learn
Subtitles certainly do record on a modern PVR and can be switched on and off at will. That's assuming they were broadcast with the programme in the first place.