I think that a good 60-80% of their customer base would not have even known Sketch existing until it was featured on the App store. If they feel like now that Apple has done enough marketing for them that they can survive without it fine. But they seem to forget they'd be in the complete backwater of unknown software without the App store.
Guess they don't think marketing and distribution storage/bandwidth costs 30% of sales. Maybe not but I'm guessing it's close.
What marketing has Apple done? You mean hiding most Apps beneath several layers of obscure searches and lower echelons of Apps? Only the "TOP" Apps ever get any placement and if you don't know what to search for, you probably won't find it! The iOS Store has gotten worse as well. You used to be able to browse huge lists of Apps (text lists with one on each line). Now they show one app on the screen and you have to swipe to see the next one. HOW THE FRACK are you supposed to browse any amount of Apps to look through with THAT system? Let's face, Apple has gone to hell lately. They've redone everything just to give it a facelift, but sadly the changes are more than skin deep and they've managed to make everything HORRIBLE to use in the process (not just looking bad with that "flat" system of theirs).
I really don't know how Apple keeps getting high consumer ratings given all the bad moves they've made over the past few years. I can only imagine that Windows 8.x had a lot to do with it (even worse complaints). With Windows 10 not sucking quite so much (other than being spyware) and Microsoft putting an actual effort into making their own high-end hardware (something 3rd parties never wanted to do since it was a race to the bottom), I think Apple isn't going to keep reaping Mac sales in that kind of an environment. They need to get back to basics and restore basic FUNCTIONALITY first and worry about new features and graphics makeovers later.