Eric’s article covers the basics of why people might like a curated/closed app store setup:

But inherent in the [store] experience is that what you find on the shelves has been selected and vetted by the person or people running the store. That doesn’t just mean favoring one brand of soap over another, but also deciding what to carry at all. Your hardware store doesn’t sell flat-panel HDTVs. Macy’s doesn’t stock six-inch PVC pipe. Target doesn’t offer porn.

And the opportunity that the web stack provides for alternatives:

For starters, imagine this: you have bought a number of apps at your favorite [web app] store and installed them on your iPhone… Then, two years later, you decide you’ve had enough of Apple and want to move to another smartphone. Once again, your apps and data go with you.

I love native apps, but I’m looking forward to this future.