There were definitely castles which were built to withstand sieges. Like Krak des Chevaliers and other crusader castles. Of course it was preferred if seiges could be avoided but I do not think your pedantry about fortress vs castle matters much since there were many types of both.
On the contrary, I am quite aware of those, but op is not. Krak des Chevaliers might not really fit the profile of castles in clasical meaning, but belong to a very specific niche of fortifications of military monastic orders in Middle East.
As for castles in UK - these aparently are representative castles and not really only fortifications. Even the smallests castles in UK were mainly used for something that was manor estate of a local royal family.
