I agree with you. This is why I will probably never go contracting. These my observations:

You have to be an expert in the required area. Example: you have to be a Java Developer. If you are a software engineer that uses Java as one of your tools, it's not gonna fly, because god forbid you won't know by heart some java specific library/method/quirk/etc during your interview - this will be immediately filed under as a "NO" under "can hit the ground running" section, no matter how good you are at software engineering as a whole. In the end you will work with handful of "proven" (read "old, outdated") tools and become an expert of handling all kinds of legacy mess.