I've purchased a few software packages that offer yearly subscriptions. These subscriptions will include any updates or plugins for that year. There is of course the typical software for sale that is simply the program itself. If the vendor does come out with a new update to the software you bought - you have to pay a big price for it. So let me ask the "business sense" side of your brain this question: If you created software or even an online service, which "sales model" would you prefer to use from above?