I guess it is a nice option to have but site owners should think long and hard about the particular dynamic that persuades users to visit and contribute comments to their site.

I suspect that for many commenters the link is seen as a small, mostly symbolic, "payment" for contributing their time and thoughts. My own site gets quite a few visitors from the comments that I make on various sites (mostly probably motivated by the question "Who is this asshole?") and, although that is of no monetary value to me, it is certainly something I am aware of.

I also value being able to quickly visit the site's of other commenters, so, yeah, I suspect that removing links from comments that you otherwise judge to be worth publishing is likely to make your blog worse, not better. If it is spam, delete it, otherwise let it stand.

One funny thing I have noticed is that, very occasionally, a site owner will remove text from my name, the "from WordSkill" part, seeing that as a form of spam, although I only use that in order to avoid people confusing me with Automattic's Donncha O'Caoimh - it would be so unfair if he was to get blamed for my rants :)