I delete all links in comments on my Hubs. I don't want to worry about what the link is. Very rarely (VERY rarely), if I get the sense the person is being very genuine about his reason for leaving the link, I may let it go through.
Most of the time, it just looks to me as if someone is trying to be particularly clever about adding his link because he's heard "Don't leave a link without saying something relevant". In other words, I tend not to think the positive comment was genuine and/or aimed at offering something to the Hub/discussion. (And even if it was, I just don't want to get into having to try to think about links and whether they'll in some way hurt my "algorithmic reputation". I do enough to damage that, myself, without the help of strangers. lol )
I'm not saying my way is "the best way" - just that it's yet one way some people handle the situation.