Steve Jobs had the similar idea so he opposed the idea of App store initially but as we know he gave up and we know the result. I think idea is to present "containerized" experience so the user thinks they are dealing with the app exclusively. There is some personal appeal to app whereas web page seems like a general purpose app which some users feel they may have subpar experience.

I think non-techie people are more accustomed to "exclusiveness" where you just reach the app directly as compare to having the choice the entering the webpage address or even clicking a bookmark. Sometimes it is more about human psychology than technical issues.