Here's the thing. You have to have collaborators in order to have collaboration. The implication in the readings I have done recently is that if you put something out on the web, someone will respond. If we are going to use the read-write-web with our students we have to let them know that there is no guarantee that someone will respond to your writing. There is no way to predict if what you write, or publish, or ask questions about on the web will be responded to.
I don't mean we should discourage them from posting, but let them know that there has to be a reason to write other than to gain an audience. Without putting something out, you will certainly not make connections. We should also teach that one of the responsibilities of being part of a community is to give, to participate. So part of being part of the world community online is to make comments where appropriate.