Comment spam yet again

In the last few days I’ve been getting maybe 5 or 6 bits of blog comment spam through each day. The weird thing is that they’re not advertising viagra, cialis, dodgy websites, poker or anything like that. In fact, they’re not really advertising anything as such, but random phrases within the comments are linking through to various legit URLs. What is the point of that?
I’ve been deleting the comments as they come in since they’re just garbage and will only (in my opinion) encourage more spam comments if left alone.