Bukkit/CraftBukkit — comment on commit ce8dd57fff414afb761b4fd2ab3ed27902ae5dd3
File:  line 0
By Cogito:

This method was never intended to get all players who have once logged in, and are not logged in (as one might reasonably think). This is because OfflinePlayer is (perhaps confusingly) a super class of Player that encompasses both online and offline players. The method getOfflinePlayers, as noted in the javadoc, is designed to retrieve a collection of OfflinePlayer objects, representing every person who has ever logged in.

I am definitely for renaming these classes and methods, but that is a big, breaking change. Renaming the method is perhaps more easily achievable, and should reduce confusion.