We are hosting KhanApp ourselves. OpenAppMkt provides easy ways for end users to install or bookmark our app onto their phones. Plus it gives us install numbers and reviews etc.
That last statement a key benefit of an app market. Tangentially, I've seen developers driven nuts by downvotes for bugs they fix in no time, but that can take days to get approved with native apps. Or on android, by fragmentation issues in which apps don't work well on certain phones.
You may host it but if i visit khanapp.com on my android it tries to make me install openappmkt. I should be able to just use the app. It's html, I have a browser that supports html, so let me use the app.