I know this isn't an answer, just an opinion. I think that 'hand-luggage' should be just that. I'm fed up with people having small sutcases (on wheels) classed as 'hand-luggage'. Having had one of these heavy bags fall on me while on a flight, because the pillock had to have a small suitcase to enjoy his journey (and I have to say it bloody well hurt). They can be dangerous and also are they really necessary?
To answer your question, you would hope that any responsible airline will allow a few more kilo's on the allowances.