I purchased this product on day one, and I think how it is handled is really very fair when you consider the following! ....
SMP V1 Full price + every update to this version was free up until SMP V2 was released, than a discount price was offered and all updates to this version were free.
The same process was continued into SMP V3. A lot of things were updated in these previous versions and I am delighted to only pay the reduced price for version 4.
Nobody in their right mind is going to assemble a group of developers and build something like SMP sell it and continue on improving (for years now) for nothing!
Business just doesn't work like that, nor does common sense!