During a recent trip to France we had to do the security line thing after checking in at CDG. While we moved along the Disneyland-like serpentine line there were security agents stationed at the turns.

One of their duties was to keep an eye on carry on bags and FREQUENTLY took people out of line to measure their bags. If the bags didn't fit in the sizing box they were sent back to check in to deal with it.

The end result was NO large or heavy carry on bags at the gates.

In the USA the policies are in place but, for whatever reason, they are hardly ever enforced. They have no problem charging for a bag that is a few pounds overweight but a carry on the size of a Smart car seems to be OK.