I don't think GF do particularly have less carbs/sugars, in fact some will probably have significantly more (I have no actual proof for this, its my pet theory)
So a small check:
My GF Biscuit breaks sat on my desk at work: per 100g: 60g carbs, 22 of which are sugars
Belvita breakfast biscuits (on my workmates desk): per 100g: 70g carbs, 27 of which are sugars.
So whilst the GF ones are slightly less, its not really a significant different.
Next check (via the internet)
Bread: Genius GF bread (it actually tastes quite nice but does tend to crumble), per 100g:43g carbs, 5 sugars , per slice: 15 carbs, 2 sugars
Kingsmill bread: per 100g 39 carbs, 4.3 sugars, per slice 11.3 carbs, 1.2 - and the slices though lighter are probably bigger, GF slices tend to be small in size
So the normal one has less carbs
Personally I wouldn't be on a GF diet if I didn't need to be, for a start it costs a fortune - £3 for a loaf of bread!
Edit: corrected some typos