I think Ryanair has a 10kg limit per bag actually (but everyone is allowed 2 bags each).
Anyway, surely the real problem lies with the size of the bags people carry on board and/or the number of bags, rather than weight? If someone has a bag weighing 8kg rather than 7kg, it really makes no difference to anyone other than the person carrying it. Conversely, it's clearly a much bigger issue when people clamber on board with 2 or 3 bags, some or all of which exceed the size limit, which they can't even carry down the aisle without smacking random other passengers in the head. And IME, VA has never been particularly strict about the latter.
FWIW, I have only had my carry on weighed by VA once - at Maroochydore.