Exactly Wiz. Happens in Oz all the time. It causes the odd problem as well, mainly in Perth with unforecast fog.
I suspect that this is still allowed due to 1. the relatively low traffic density in the areas where it's an issue (PER, DWN, ASP, BRM) and 2. the geography. Holding an alternate for PER is the same as holding Oslo as an alternate for Manchester....
It's partly mitigated by the fact that we have compulsory holding fuel for temps and inters which as I understand the JAA does not.