This isn't accurate. It is more like:

Customer: I want a table with four legs.

Dev: Ok, give me 2 days and it is done. after 2 days Here's your particle board table about 1 meter off the ground with seating for 4.

Customer: Great, but it would be nice if it could seat 6 sometimes because we sometimes have guests.

Dev: Ok, give me half a week. 3 days pass Ok, here's your table for 6, we had to change the material to wood to make it more durable and unfortunately it increases the cost.

Customer: No way I'll pay extra for wood. What's wrong with particle board? And the texture of this wood is too noticeable, the texture has to be more subtle. And we want to minimize the size to a table of 4 when the guests are not around so we can have more floor space.

Dev: Ok but expandable tables are significantly more complex and I don't think we can do it with your cost contraints. Can you consider increasing the cost?

Customer: What are you talking about? When I asked the Indian shop down the road they said it was possible at this cost. Are you lying to me? If you don't fix this and deliver then I want my money back and I'll just go with the competition.

Dev: Ok, we obviously can't compete with that price so here's your refund. But we highly don't recommend that shop because you will have issues with the table.

Customer: I think everything will be fine. Good luck to you and don't try to upsell me.

6 months later

Customer: Here's the table the Indian shop built. It sometimes won't collapse and they can't figure out what's wrong with it. Can you fix it?

Dev: Ok, we can take a look... You see the problem is this rail design is not fit for these specifications. We can fix it temporarily but in order to fix it permanently we have to rebuild the table top surface which means only the legs will be reused.

Customer: What do you mean? Can't you just install new rails?

Dev: You see, particle board is too flexible a material so over time the fasteners will fail. That's why we recommend wood. But you didn't want to pay for that in the beginning so we didn't want to continue with the contract.

Customer: Fine! Fix it, we need the table next week for a dinner party. How much?

Dev: Our backlog indicates we're booked for the next month. So to prioritize this job we need additional compensation as we'll temporarily have to hire additional help to satisfy demand.

Customer: Are you crazy? I can get 2 new tables that don't expand for that price. This isn't rocket science, I'll find my own way.

6 months later

Customer: We need a table. We're ready to pay anything.

Dev: Oh, you're in luck. Expandable tables are now free of charge. We only charge an installation fee and optional warranty fee if you want us to fix potential issues after delivery. The only catch is they only come in white.

Customer: Excellent, but what about brown? And since it is so cheap now can't you make it height adjustable?

Dev: The brown configuration is a small additional fee but the height adjustable feature has to be made from scratch as it is new technology. It is quite expensive because the motors have not been validated yet, so we have to do a qualification test on each part.

Customer: what? just give me the white table and I'll go talk to the Indians again.

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Software often has expanding scope and new "innovative" requirements. It is almost never the case that we have a fixed deliverable; once the customer has a solution, they immediately want something else improved. This flexibility manifests on additional R&D costs for new or customized technology.