Why don't RSS Readers support kill files?

As I was flowing through my RSS subscriptions in Google Reader I was struck for the millionth time how much everyone likes to write about "All Things Twitter". "Man, I wish I could just zap these items from these feeds" I thought. Then it hit me that I used to do that all the time in my favorite Usenet News Reader nn nearly 20 years ago! Usenet programs nearly all supported killfiles, and it was great. What is a kill file? From Wikipedia:

A kill file (also killfile, bozo bin or twit list) is a per-user file used by some Usenet reading programs (originally Larry Wall's rn) to discard summarily (without presenting for reading) articles matching some particularly uninteresting (or unwanted) patterns of subject, author, or other header lines.

That is exactly what we need in our RSS readers. Please, please, pretty please?