Quite true. To modify and add to Apache's default page list, open your configuration file, and look for "DirectoryIndex". By default, it will just include "index.html". To support both, change it to:
DirectoryIndex index.html index.shtml
These are searched for in each directory *in order*. On my own personal installation, I use SSI's exclusively, so my index.shtml goes FIRST in that list. Again, doesn't make much difference for a smaller site, but if you're getting a boatload of hits a second, it's a minor improvement.