Firstly, not all products on this model die out - one example is PureBasic.
Also, I agree with other comments that it seems upgrade prices are too high compared with the full product.
Also, other products that do charge for upgrades, normally charge for full version (e.g. 3.0 -> 4.0) upgrades only, and not point releases (3.0 ->3.x).
Finally, if I pledged for the KS and I get 3.1 when due, is there anyway to get that Steam Indie Edition as well either for free (preferably) or for a low atractive price?