Also I think the game is at $12 something at the moment (PC/Steam version)

The reason why they don't to that is because the computer version has a bit more stuff, better graphics, the ability to run with more parts, part nudging ect and when you buy the iOS version, you don't get a whole lot of those thus the price different I do believe they had a discount on the steam version if you had bought SP on iOS, but this was when they first put it on steam, I just recently upgraded to computer and I had found nothing on discounts on it, yes I agree having a small discount on the game when upgrading would be nice

no they are 2 different products