I think the big difference is that they come with the OSes that those types of people are likely to use. And being stores, they provide software that package managers are unlikely to provide.
I think package managers becomes less useful to average users when you can't expect all of your software to be there.
On Android they sometimes do install OS level stuff (libraries, etc). I think he has a good point.
The biggest difference I see is that package managers on most Linux distributions are designed to be extensible to support other sources. Application stores generally are not.