Isn't a prequel by definition something that was released later than the work it chronologically precedes in a narrative sense? That is, something does not become a prequel just because it gains a sequel, it just is the original.
That little pet peeve aside, linking connected works together makes a lot of sense and it would indeed be handy to have it somewhere directly on the the page of the manga in question. Usually someone in the comments links it either way though, and it is not too hard to dig through the artist's page most of the time. Just one of those small conveniences.
