This is interesting.
Not sure if this is valid, but it seems that MS allow discounted UPgrades and DOWNgrades if you buy into particular sw product family.
In other words, buy a version, buy any other version cheaper. Or perhaps buy a version, then you can buy next UP version and any DOWN version cheaper.
So they see each version as a different product and if you have one in the family, you get discounts on the others.
Does that sound right?
As to the 49 -> 69 example, would that be a CPI thing? Simple inflation, just as with cars and washing machines.
BTW, before buying PureBasic, I bought VB.net (1.01, IIRC). I paid Aussie $50 for it, from a Microsoft authorised dealer who was recommended to me by Microsoft. Reckon I could get a discounted VB6 based on that purchase? Although I am not sure what I would do with VB6.

@}--`--,-- A rose by any other name ..