You don't need it, but it makes things a hell of a lot more convenient. When I run Linux, I don't Google "linux media player", I just search the repository and install things much easier. If I googled "linux media player", I'd have to sort through various unrelated sites (reviews, howtos, spam/malware, old versions on different sites, forums, etc). When I search an app store/repository, I just get exactly what I want. It's less of a noticeable benefit if you know exactly what you want (because you can usually look for the app name and find their site), but it's helpful for searching for a category of apps. Additionally, it's nice to have a simpler update system. Updating apps on Windows is a mess, and I know I should really do more about it, because apps that don't include update functionality generally don't get updated.
you make a fair point, making the distribution easier is a nice feature. I still would have preferred a slightly more open approach however. How about defining an installer protocol? like install://url.to.my.servers/my.app.installer.json.or.whatever.format and then my browser could have the app installer for my OS registered on install:// urls. that way the installer format could be cross platform, and not controlled by any 1 company, but still be an easy point-and-click on a website without the hassle of running other things etc?
Then if you want the trust that the verification of apple gives you, you should make sure you only download software from apple.com, but the whole system is still more open and accessible by being online on websites rather than specific to a piece of software running on OSX.
