I brought this up briefly on the list but I thought I would submit a formal issue for it.
I think _rewriteBase should be automatically prepended to the routes. On applications that would be distributed via download it would be easier to define generic routes. An application with routes like:
/user/:id
/news/:action/:id
would never require a base path to be set in a config file or anything, as opposed to
{$settings->basePath}/user/:id
{$settings->basePath}/news/:action/:id
You'd have to do a few checks for beginning slashes, but I think it would be a neat change coupled with the automatic _rewriteBase detection that was recently added.
Everything you were required to do was to set a correct rewrite base and set the rules without it. Thanks to todays commit you don't have to set it anymore as it is detected and set automaticaly.