Yes, it is hefty, because I already paid for Sketch 2 and I still remember the time when Apple was peacocking that "buying from the AppStore you get the future updates for free"
You can't stay in business selling one version of your software to customers long term.
If you can't stay in business then there are no new features and the product dies.
I understand when laypeople don't understand the software business, but you expect more from the development community.
I'd be curious to know if you have a citation showing that Apple ever made this claim.