steve,
there are two main types of sweet corn, not to be confused with commercial corn! there are sub sets underneath like yellow, bi-color, white, etc
one type is the fresh market varieties, that sub groub has some different desires: the guy who raises fresh market in GA, FL, CA and then ships to the north, he wants a fresh market that will still stay sorta fresh after transportation, taste is not as big of deal if it looks stale in a day. the other component of fresh market is the road side vendor, he wants everything to revolve around taste. he picks it, and brings it straight to the consumer, no desire for freshness/productivity/easy of processing. there are varieties to meet both needs.
the second group are the processor varieties. these are selected for attributes like: yield, kernal depth (since its a automated knife cutting the kernals), storability, etc. most products in agriculture are better if grown fresh and sourced direct. but city folk sometimes dont know what fresh can be like so they are content with what they get. one side note, sygenta at one time was working on breeding a tomato that took the shape of a can so it could easily be cut by taco bell's dicer, you tell me how much taste factored into that buying desicion? not necessarily a bad thing that these guys are very efficient, that is what the consumer has demanded, not taste.
the actual varieties themselves are generated by a relatively small group of companies and most are propietary.