I think a lot of people had that theory in their head the whole time they were watching it and just refuse to accept that they were wrong. Kind of like a "See? I called it years ago!" attitude.

I'm with you though, I can't help but judge someone who watches a show for that long, is explicitly told in the finale what happened, and still completely misses the point. I had a coworker who fairly recently was going on about what a waste of time Lost was because the ending was so bad. I told him his interpretation of the ending was flat out wrong and why, but he wouldn't accept it.