If you're hired to build a 2 story home for 75K and you see that's not enough money...
The situation is a little bit different. You make a plan for a village, and tell the contractor that it will cost 2M. The final part of that village is a house for 150K, that some people are really looking forward to (let's say some sort of community building). But the contractor can't come up with the 2M and is 75K short. What do you do? Do you tell the contractor that you will then just make the rest of the village and leave out the community building altogether, or do you offer to make the most of that 75K and build a small shack as community building? I believe that in this case, that shack will actually make the contractor happy, not angry. After all, a small community building with less possibilities is better than no community building at all, right?
They created the design...
This part of your reply fails right in that first sentence. When they started the KS campaign, they had a global idea of what they could make, but I sincerely doubt that they had created the technical designs (they didn't even have the GM stretch goal until later in the campaign). Only now that the funding is certain, will they sit down with their designers, discuss how they can do it and come up with an actual technical design plan. If they had less money, then that design plan would just become a lot simpler... but a simple plan with less options is still completely different from "half a plan".
One very simple example: a full Game Master mode could have the option to "create your own maps" (with the supplied editor), while a slimmed down version would only have the option to choose from 10 pre-defined maps... still fully functional, just less flexible for the user, and a lot cheaper to implement.
