The difference between Ryanair and most other carriers (except FlyBe) is that Ryanair will charge you even for that 20 kg. (It's a nominal charge for 20 kg, if you go over that you pay an arm and a leg). And I've noticed that since they started charging they have become a lot stricter over hand baggage limits.

Oh, and I've seen a Ryanair "hand baggage weigh point" once, at one of their regional airports, just before the security checkpoint. So the old well-known trick of getting someone else to hold your other piece of hand baggage won't necessarily work with them.

With rgards to legacy carriers...I've never put this to the test, but people tell me that you can usually get away with 25 kg.

As for "Those of us coming in from US/Canada already exceed that"... there is no law saying that you HAVE TO take your full allowance. Just travel light and you'll be OK!

Ryanair is pretty awful BTW.