Marketing and versioning is often done in threes because that's the minimum number you can use to take advantage of the psychological aversion to extremes that people have.
It's well known that if you have two versions of a product with some purchase distribution, you can often "force" people who otherwise buy the cheap one to "upgrade" to the more expensive one by simply adding a third super-expensive version.
There are people who will pay for the premium third level, but often more importantly, it causes psychological angst in anyone who wants to buy the cheapest, often forcing them to upgrade.
As every mathematician knows, two is the most magic number. A lot of strange things happen with two. Take fields of characteristic two for example. (That is fields were 1+1=0.)
It's well known that if you have two versions of a product with some purchase distribution, you can often "force" people who otherwise buy the cheap one to "upgrade" to the more expensive one by simply adding a third super-expensive version.
There are people who will pay for the premium third level, but often more importantly, it causes psychological angst in anyone who wants to buy the cheapest, often forcing them to upgrade.