I agree with a lot of your points
@Scott-C; the more I read your post, the more I feel that you're exactly right.
It would be great to go in for a meal and have the nutritional info stamped on the menu; similar to Wetherspoon's - although they lack carb content.
A facility like this would be very handy, although I agree now that making it compulsory would be a little extreme and not all that easy for some small business owners. It would be easier for corporate chains, as most of their food is pre-prepped and reheated.
What I would like to see though are more business displaying nutritional info of their meals; if they can include carbs then excellent! Teaches me for not reading things properly first thing in the morning I suppose. It's still an excellent idea, but pretty hard to implement across the board for the reasons you've stated.