Exactly, which is why I'm still using Knockout, it's been around for a long time (for a javascript library), values backwards compatbility and is still developed (only a few developers but they are all committed).
It's also just got a lot faster (3.4 had huge speedups) supports HTML5 components and supports IE back to 7 (while that's not a requirement for me it's nice to know the tools you have will work if you need them to).
There are features in newer libraries I like but taken in balance I like been able to grab the code I wrote 2 years ago and have it still work with knockout's latest version, to me that is it's killer feature.
Also there is this http://knockoutjs.com/spec/runner.html
