ex: look at rdocs for sinatra via gembox:
Errno::ENOENT at /gems/doc/sinatra/0.9.2/index.html
No such file or directory - /home/rdp/installs/mbari_gembox_187/lib/ruby/gems/1.8/doc/sinatra-0.9.2/rdoc/index.html
syntax is a good example
Rdoc only displays if there is an RDOC directory and the has_rdoc? gem spec option is checked. Closed by 44673f9
Also, gems now reload if the mtime of your gems directory changes
Hmm. The reload is great and awesome. unfortunately it appears from recent changes to Gem  that has_rdoc is now "deprecated and ignored" [i.e. it generates rdocs for every gem now]. Keying off the existence of doc/index.html might be a surer way.
Thanks for your help with this!