there's already a discussion about this article here :
https://www.mobileread.com/forums/showthread.php?t=49371
there is a suggestion that the download limit might actually be a device limit, although it's still unclear to me since the article clearly suggests otherwise.
an easy way to test the theory would be for someone who has a kindle to download one of their books repeatedly (ideally, one they either don't plan to re-read, or one which they have backed up drm-free already, if they might want to re-read it) and see whether they eventually lose access to it (for downloading from amazon's servers). no way to know how many downloads it will take to hit the limit but i get the impression it shouldn't be more than 10 or so (maybe less). in one of the comments, the author claims to have done this, and lost access after a certain number of downloads.