If you play as England in ck2, and manage to take some chuck of holdings and provnices in Europe, but just before the end, you manage to lose all the provnices in England(invasion, revolt), you will start with navy ideas in EUIV even if you don't even own a single province with a port (hypothetical). But after all, most of the Europe has its own nationl ideas, expect for South east Europe, Ireland, Brittany and some other minor/non important parts, so I don't see where is the problem here. If you don't like it, mod it, or they are going to release this as a DLC (which would be stupid).