No matter how good your application is, no matter how novel, how brilliant, how special -- none of it matters if you don't have anyone to use it. The iOS App Store changed the way developers work by providing a streamlined channel between software developers and potential customers.
Consider my APIkit scanner application. After opening the app to public beta a few months ago, I may have gotten about 200-300 users. Total. (And a grand total of zero feedback, but that's a completely different gripe about public betas.) Contrast with App Store.
As far as I can calculate, I have now shipped well over a million apps on App Store -- that's extrapolating from the 600+ thousand copies that iTunes Connect tells me I've pushed out in the last six months, not including updates and such -- just individual purchases. And no, I haven't earned much from those purchases because nearly everything I've put on App Store to date has been free.
That's not the point.
Being able to touch that many people's lives, and offer them a few nice utilities is the point. Even as a primarily free developer, it's brilliant to know that I can create apps that matter, that entertain, and that help. I love when people write me and say: "This app is fun" or "helpful" or "silly" or "delightful." And I wouldn't have been able to do that without App Store.
I've got a ton of lonely little Mac apps sitting on my back burner that I think can help a lot of people. And now there's a chance that I can share them in a meaningful way.
Now, step back and consider this from a business point of view. If App Store has done this much to help me reach people as a free dev, consider what it can do for a Mac developer's bottom line. App Store sells apps. It connects customers to content and developers to an audience. And that's why it matters.