Pegg does a better Scottish accent than I do. And I'm Scottish.
There's always some protective madness when someone does the accent, but Pegg's not playing a guy wandering through the Barra's looking for dodgy DVD's. He's a professional aboard a mixed crew. He sounds pretty much like the people I know in the navy and army who's accent tends to loosen up to communicate, or artists/actors who've had to adjust to reach a wider audience.
I had to adjust my accent just to tour England and have lost my regional tones for something a bit more 'generic' (BBC Scottish-ish) over time.
Compared to my dad (who's been living in the US for around ten years and who's voice has become a strange blend) that Scotty's accent's held up fairly strong.
How dare you, i have never walked roon the barra's looking for DVD's, it was Atari St 520 games, £2:50 each, don't hate me. lol
But yeah,i doubt most people around the world would pick up everything Pegg said if he had went full Glaswegian, but he has a very good mix of both a Glasgow accent like mine,(aye, naw, kertoons, watter, gress, mulk, doon), and a actors version of a Glasgow accent, (Yes, No, Cartoons, Water, Grass, Milk, Down), which it think works out very well.