Someone noted the French don't wear vests and only from my limited experiance of one French crew at Duxford I know they don't mind smoking under their aircraft either!! So just because they don't doesn't mean it is [not] a good idea.
(1) I'm sure that you would agree that one aircrew is a grossly insufficient sample population from which to derive any real idea of a nation's safety practices.
(2) The French are not alone in this absence of vests. As far as I know, it's not done anywhere other than the UK ... at least, I have not seen anyone wearing vests in Canada, Australia or the USA. It would be interesting and instructive to compare the respective national statistics re the number of collisions between a/c and people on the apron. If the UK stats are, say, 1/3 those of the other countries, perhaps it's a good idea; otherwise, an obvious waste of time.
P.S. I guess those in favour of high visibilty clothing would also be keen on mandating that all aircraft must be painted in solid dayglow orange? If not, why not?