I don't think I made my point clearly. I think having a user install the app can get them to return to it, but only if there's something remarkable about it. Providing relevant information or amusement is remarkable. The vast majority of apps fail at this. After checking out both of those apps, I think they succeed, but only for certain niches. And the numbers agree: the Audi app I tried has more reviews than Tweetie does.
It's commissioned mobile interfaces for websites, done as native apps, which seem to be asked for by many website stakeholders, that I'm ranting against. If there isn't something remarkable about the app, yet users install it and don't remove it, I don't think having the logo on peoples' iPhone home screens helps market the product very much. It's like a tiny banner ad with a lot of impressions going to the same person.
I looked at the websites of both of them on my iPhone. thenorthface.com is flash. 'Nuff said. audi.com works, but isn't tailored to mobile devices. They do have a mobile site, but I only found it when I followed a link in Audi's app. I don't know how I would have found it otherwise.
I don't think the app development slowed down the development of their mobile sites. I think that was a separate issue. I think the apps are a good idea, but that they should build out mobile sites as well.