Sometimes Scottish people get subtitles too.
Aye! :-)
Well, the dialects are impossible to understand, I guess, unless live in a neighbouring area, like LE with Dutch, but even Scottish English can be difficult. But it's a great thing that people still speak those accents and dialects. All over Europe the dialects are sadly on the fade, and young people don't even want to speak with a local accent anymore. Everything is somehow streamlined by the media, Estuary English for everyone, or whatever the standard is in Germany, Italy or wherever.
But honestly, sometimes I find the subtitles useful for some varieties of American English, too. You know, the type where they pronounce the word banana with 3 r's, as Martin Amis put it.