With coursera I think it depends on the area.
There's an algorithms I and an algorithms II course, for example.
I'm starting Crytography I next week, and expect that to have a follow up as well, and Analytic Combinatorics, Part I is in a couple of months.
The logic course that finishes up in a week or so though, that one seems to come out of nowhere and not have much of a stated follow on to it. Despite, of course, being useful for all manner of computer science.
But as for the groundings for these courses. I don't know what the answer is. I don't think the providers need to provide a basics level, especially if they are getting sign up numbers into the 50k per course. But providing basics courses or self-study pre-courses would be a good move, considering the number of people in the logic course who, unfortunately, didn't have the knowledge base the course requires.
There are some pain points coursera could smooth over, and having a better course search and course reference system is one of them.
I think, because it seems that a number of these courses are on line equivalents of off line courses, the thought hasn't been put into making the course abstracts stand on their own, but instead are just rewordings of the standard course descriptions.