Of all the unconstructive comments I've seen posted on Stack Overflow, I actually find these the least objectionable. Why?
They actually ask a useful question, and one that the asker should speak to in his question. If the link were not included, the comment would still be reasonable. In fact, it seems that the community has already agreed on this being an OK question to ask.
As you mention, "the blog post linked to is actually good advice". So if people do click on it, they stand to learn something useful. And if someone doesn't understand the point of the comment, then all they have to do is click on the link for more information. It's even better than just asking the question alone.
I agree that these types of comments are wielded like a particularly "blunt instrument", and that they come across as a little bit harsh. But honestly, the questions I usually see them get posted to deserve a bit of harshness.
As far as the comparison to LMGTFY, I think it's a bit of a stretch. There's absolutely nothing constructive about LMGTFY: the entire website was designed to chastise and insult. It's inherently disparaging, regardless of the usefulness of the search results it (eventually) produces. In other words, the process subverts the ultimate goal. That's not the case with these comments; neither the presentation nor the result is intended primarily or exclusively to insult.
At some point, the asker is going to wonder why the question got closed. These comments can serve as their explanation, in lieu of an extended Meta discussion.
TL;DR: I think these are OK. They're nothing like LMGTFY because they actually provide something useful. If you see one that is particularly useless or unconstructive, just flag it as usual.