Even if you ignore the way that the types of template instantiations are (for good or for ill) unrelated, these two types are not compatible. Say this particular conversion were permitted. You have your function. (String literals are const char * .)

    void blah(vector<const char * > &xs) {
        xs.push_back("blah");
    }

And you have the code calling it:

    vector<char * > xs;
    blah(xs);

And that would not be valid. The rationale for the conversion rules for pointers to pointers is based on a similar sort of problem. (In fact I think it's exactly the same problem, at any level, but that only just occurred to me, so perhaps not.)

(This isn't to say there aren't other similar sorts of conversion that would be safe, and that the language perhaps should support, just that this isn't one of the valid ones.)