I had a discussion with my SA which seemed to indicate this very thought. I mentioned that I had been looking for some Moras for sometime and that there seemed to be some demand for them. He stated this was a little funny because the Moras did not sell very well (at least to his knowledge), which is most likely why they were discontinued originally.
Though they don't always seem to discontinue shoes based solely on their sales. They seem to have at least a little bit of the "take it away to increase the appetite and reintroduce it later" approach at times. Sort of like Disney putting their classic movies in "The Vault" only to be released every decade or so. Granted, some of this is conjecture, but every now and then, a shoe that seems to be quite popular will be eliminated.
Take the Sanford as an example. When it was reintroduced after being discontinued, their webpage said the following: