Hi @Abhishek Dewan,
Thank you for that link.
As I said if you need money (which you obviously do) then offer a full version for x $ then provide free updates for that version, and offer an update for y $ to the next version. In the old days of software a new version was released every about 18 months.
Most people do not mind to pay for updates, the subscriptions makes people look for other vendors, me included.