You cracked me up :) I was chatting to another programmer about this - he broke it down like this...

It's like making a car 10cm longer. To change the paint we'll spray paint it and you can pick it up tomorrow. If you want to change to leather seats then it’s going to be a few days work come back at the end of the week.

But if you want the car 10cm longer then that’ll cost millions – and, likely take a year to complete.”