I don't mind if people do it on my hubs in the comments if it is relevant to the hub and insightful. You can tell if a comment is spam by just reading the comment, or if the link is totally off topic. Then I delete the comment.
What I think is complete crap and snobby to the max is when some people on this site delete your comment even though it is clearly not spam and the link was one of your posts that either supports your comment or supports the hub being commented on. That's just completely rude if you ask me and I will never link to that author on ANY of my hubs for the rest of my time on hubpages. Interlinking relevant content HELPS hubs and honestly doesn't take away from the other authors hub by having a relevant link. Actually helps in pagerank to be quite honest. I have had numerous authors delete my comments that were like 2 paragraphs long on their hub topic and I put in a link to one of my hubs to support my comment and their hub. Some authors are OK with that, and some just get ridiculous and delete them with a smile. Oh well, some people just don't completely understand what spam is and think that anything with a link in it is automatically spam. So naive... I've been around the block so to speak with interlinking, spam, comments, and links in comments. I run 4 different websites outside of hubpages that are doing not bad. Just my 2 cents on the matter.
Sorry for such the long comment but I feel very strong about this topic and am actually glad you asked the question. I TOTALLY SUPPORT putting links in comments to your hubs provided they are of high quality, helpful, and directly related to the topic at hand and being discussed. I don't think Hubpages themselves make linking to your hubs in the comments section illegal to say, but spamming definitely is not supported by hubpages or any authors that I know about. I hope that last bit there answered your question a little bit. And if your comment gets deleted and it is a good comment and your link is relevant, don't even waste your time commenting on that authors posts. They are just being rude hubsnobs. Support other hubbers that actually understand the matter of linking and helping brother and sister hubbers out.
And have a wonderful day!