As to why the USA do and the UK doesn't, the passur website says it all:
http://www.passur.com/am_airport.htm
Sorry SB001 but it says nothing about keeping spotters happy.
More for community awareness of flight paths and such, which isn't a bad idea. Maybe for community relations it wouldn't be a bad idea for places like STN or LHR.
I can see what SB001 is saying: 'What's the harm in having this info available?' (the law aside). It doesn't really pose any greater risk in security. I mean, a lock will only stop an honest man. If some nasties are intent on doing harm, would not having this sort of thing really stop them? Then again, do we want to hand it to them on a plate?
Anyway, enough said.
Let the status quo remain