That whole secret identity was pretty much a hard-and-fast aspect of Superman's continuity until the Byrne era. Since then, having a few people here and there know who Supes is - and not necessarily folks that he chooses or who are central to the continuity - is something they've played with from time to time. Also since the 80s, Lois and Clark's relationship has been treated as one that evolves; it was held in a pretty rigid template from the 40s through at least the 70s.