This is a reasonably innocuous strategum that goes alongside the dictum "Never read the bottom half of the Internet".  Anonymity brings out the nature of trolling, which we all know can get nasty.  Marketwatch is trying to implement a readable comments section.
Though, I will hasten to add, there are different types of anonymous user names.  One type which just yells out "troll" and another that spells out "reasonably coherent commenter".  Perhaps a better answer would be to accept anonymous usernames, but only if they meet a certain threshold of acceptability.