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.

A sample comment from earlier today:
your site is a very nice source of info. think that will make relief: , Beautiful, Good, Good nothing comparative to Collective black girls on their mission , when Pair Hope Grass Make thins that excited you at 14
The links go through to The British Museum, Google, Crystal Palace Foundation, The Natural History Museum in London, and several other perfectly reasonable sites.