I suppose that privileges are no concern of moderators, and that therefore nobody from philosophy.se can change anything about that, but I was wondering if getting the privilege to comment that late was useful. In the end new users post very short answers, that we transform into comments because they don't fulfill the answer standards. And as children nowadays don't bother to read the section on good questions and answers (pure rhetoric, I suppose most of them do) we're getting swamped with short and vague answers. What are we going to do about that?
In general, I agree with you on this; I myself have had to write answers where a comment would have been appropriate because I didn't have enough rep (on other sites). However, I think the idea is that 50 rep is just the right level where it takes just enough effort to discourages most spammers yet not hard enough for a person to obtain in one day (even one hour) if they wanted to. However, given that you can post a brand new question with no reputation, spammers can simply do that instead. So I'm not entirely sure of the rationale.
Privileges are of concern to moderators, and we want to do what we can to make Philosophy.SE a good Q&A site for philosophy. But until we are out of BETA, our power to change anything will be limited at best. If you think this to be a serious problem, consider raising the issue on meta.stackoverflow and you'll more likely get responses from longtime SE veterans who can provide better reasons why 50 rep is the requirement, and possibly a response from an Admin as well.