It's that you haven't used C. Learning C teaches you something about programming that other languages can't. It teaches you ways of thinking about problems that are useful even when you aren't using C.
This is true of most languages, and probably most true of Lisps and MLs. If you've never learned a Lisp, I also would consider you "not an experienced programmer". Not "an inexperienced programmer", and you may be "an experienced <ruby/python/garfunkel> programmer", but I think you are "not an experienced programmer". You should also use Perl at some point, for example. By the way, it's awesome that you want to learn more, that's a very good sign. (Again, this is all very heavy IMHO ;-)
In C's case, some of the things you learn are pointers, memory management, portability, simplicity, filesystems, build systems, etc. These are usually things that are handled by other languages, or that other languages discourage you from thinking about. Other languages will have made choices for you about how to hide these details, and it's often useful to have made your own choices about such problems at least a few times in the past. Otherwise you may end up blinded by the choices made by others.