Well, first, all pages generated by Abantecart can be indexed whether "seo friendly" urls are used or not unless blocked by robots.txt or some header element respected by whatever bot is in question. Be aware that if mod_rewrite should fail for any reason uses will have trouble reaching such URL's, and that using this feature WILL increase the probability of a mod_rewrite failure to some degree. This may also screw with canonical URL management, leading to problems with consistent indexing and other SEO nastiness.
If you still feel the need to screw with the consistency of the URL's, goto Admin -> System -> Settings -> System menu and look for the Use SEO URL's: configuration item there.
David