You're comparing two whole system approaches against an individual tool.

If you look at the largest SELinux user, RHEL, you find that SELinux is just a single line of defense. The philosophy that "code will always have bugs" is in play and so in addition to SELinux RHEL has many other layers of protection.

Mark Cox has an excellent list of technologies that contains all the things that come into play even before SELinux has to make a policy decision:

http://www.awe.com/mark/blog/20101130.html