Thank you, Steveau! We had a big discussion about that whole thing at the myidol forums, and we have come to the conclusion that voter turnout this week was low. This is what was mentioned there:
-1- Ryan didn't mention the number of votes cast on the show, so the number probably was not impressive.
-2- Many of the performances were bad so they probably didn't get many votes.
-3- Katherine did so well, and was told so, so many people may have figured she was safe without their votes.
-4- The producers of the show reserve the right to disqualify any votes they deem improperly cast; therefore, they may have (ab)used that power to cause a shakeup to discourage the low voter turnout.
Some of these points are conjectural, but they're all based on facts. I guess all we can do is vote for who we like, whether we think they need our votes or not. Regardless of who wins in the end, though, Katharine will always be my idol from this year.