I'm also pretty sure there is some sort of law limiting the strength of beer/cider. Although that could also be urban myth.
I think this is true.
I was once at a beer festival and there was a cider stand. One of the ciders was advertised as having a strength of "8.5%+"
I asked him what the + meant and he said it was actually about 17% but if it's above 8.5% then he's not allowed to call it cider, it gets classified as wine & it moves into a higher tax bracket so he'd make less money!