Personally suspect that the BBC blacklists. Have tried many, many times to post comments on Have Your Say, and comments on articles such as this one, where there is a place to send comments. And yet no comment has been posted. Have tried emailing them about it (early on, on HYS, for a while sent four of the same messages so that one of them could actually make it onto the forum; after reading the house rules and seeing that this probably is spamming, stopped, but haven't gotten a comment through in some time).
That doesn't seem surprising given the Beeb's obvious bias. They are probably allowing in comments which we are to believe are "representative" of general opinion. Newspapers have done it for ages.