Why does rdoc sometimes not install?

So on Prawn’s website they rub it in that we should use the local rdoc as they dont guarantee their web docs to be up to date. So I start my gemserver and I see that none of the prawn gems have installed rdoc. I have seen this occur on other gems to but not all. Is there something I need to do to get the rdoc? I did not install using --no-rdoc, etc. prawn 0.8.4



 - depends on

prawn-core, prawn-layout, prawn-security


A fast and nimble PDF generator for Ruby