It's a developer benefit if consumers feel averse to buying software that they can't re-download/update from a centralized software store (App Store, Steam, etc).
Right but that is my point. I don't think anyone would be averse to buying an app outside the app store just because it doesn't have that feature.
That could explain why someone chooses to buy it in the store if it is available both on and off the app store, but it's unlikely that there is many (any?) people out there who refuse to install an app that isn't in the app store.
I think you're looking at it the wrong way. It's not about refusal. It's not (primarily) a red line where crossing the line means you get no sales at all from the X% of people that care. It just incrementally raises the bar that customers' varying levels of desire/motivation to buy the app have to clear before they decide to go ahead. There are many other factors that probably have a greater influence on that bar, including price, convenience of the purchasing process, perceived quality of the product, etc. But that doesn't mean smaller factors don't matter at all. To get a sense of how much they matter, you'd have to measure it, but I doubt that things like license management convenience are completely irrelevant.
