In my opinion, there wouldn't be a good reason. Maybe I can find your app directly in the app store, but what the 'Web provides is a human readable (and rememberable) address. Without it, you would need to search the app store or web search for [specific product/app name] (this assumes I learn about your product elsewhere and know that the app exists and how to get it).

I myself want to know as much as I can about an app before I download it, so would always check a website. I dislike ending up on a splash page with nothing but a screenshot of the app and a link to the app store. So I don't feel that any app for any device (or any product that you are trying to sell for that matter) would not benefit from an informative, accessible web presence. After all, I need to be sold on the idea of downloading the app. I confess I do prefer web over native app in most cases as a personal preference.

It is an interesting question, and the one my mind immediately went to upon seeing this. Because, yeah, I'm not seeing how this is a good idea for Taco Bell or anyone really. I will keep thinking about it and would be interested if anyone thinks otherwise.

I guess the web could still provide information without functionality -- not too dissimilar to what the taco bell page is doing..?