Back in the WDW ticket-book days, rides were classified based on popularity. You'd think that meant that the great rides were "E"s, and mostly you'd be right. Remember, though, that there was only one park and it didn't have as many rides (I'm sorry, "attractions")*. So, a few others creeped up into that classification, rightly so or not.
*Still more than DHS and AK have now, though.