Dictionary.com defines encore as "A repeated or additional performance of an item at the end of a concert, as called for by an audience." To me, that means an encore is when the band does something extra at the end of the show because the audience demanded more, right? Then how can you call it an encore when a band has been planning it since the tour started?
There are a few bands out there who just don't do encores. System of a Down has ended their shows with no encore both times I saw them. A few other bands I've seen also ended sans encore and it was great. Now I don't mean hit the last note of the last song and the band hauls ass. Take a minute, thank your fans for being there, have the whole band come to the front of the stage and take a bow, or whatever. I just don't understand why we HAVE to have a 5-10 minute pause near the end of every concert before the last few songs.
Now I'm not saying I'm against encores, honestly I think they are one of the coolest things about a live show. A true encore happens when a band has finished and is heading to the tour bus and the roar of the fans is so overwhelming they decide "Fuck it, they want more, we're giving them more" and go back on stage to have fun.
When an "encore" is part of the schedule, there's nothing special about it... it's just part of the show.