It is not so much that mod_perl "handles" the static content, it is the fact that the webserver processes are larger due to having mod_perl configured. If you say have Apache::Registry configured to work its magic on say /perl/ then it will only "handle" URIs that start with /perl/.

That being said, I've successfully run fairly large websites (roughly 100,000 page views per day) on a site with mod_perl configured and contained a large amount of static content without any problems.

Also, mod_php would behave roughly the same as it suffers from the same Apache server child bloat, granted not to the extent that mod_perl does.