I can't think of too many instances (on StackOverflow) where someone has asked a question, where knowing if they're on 10g or 11g really affects the answer. The exception being in how LOBs are handled (I'm sure there are others), but I don't recall too many of those being asked lately. In fact of the 10 most-relevant LOB questions asked, the OPs all used the generic "Oracle" tag, and only one person used an additional "Oracle11g" tag.
Now I can think of many DBA-related tasks where it does matter, but those questions belong on dba.stackexchange.com and not SO. And if someone should ask a question where 10g vs. 11g does make a difference, they probably have a better chance at getting a good answer if it gets migrated to dba.stackexchange.com anyway.
So in-terms of a question that a developer would ask, does it make sense to still keep the 10g/11g tags around on SO?