There's a standard iOS feature for promoting mobile apps, but Google doesn't use it.
"Smart App Banners vastly improve users' browsing experience compared to other promotional methods. As banners are implemented in iOS 6, they will provide a consistent look and feel across the web that users will come to recognize. Users will trust that tapping the banner will take them to the App Store and not a third-party advertisement. They will appreciate that banners are presented unobtrusively at the top of a webpage, instead of as a full-screen ad interrupting the web content. And with a large and prominent close button, a banner is easy for users to dismiss," explains Apple.
Google implements a similar feature, but it doesn't work so well. Dismissing the banner doesn't work: when I open google.com in a new tab or refresh the page, the banner shows up again. That's annoying.
How do I know that Google doesn't use Apple's smart app banners? Here's Yelp's site: the banner includes ratings and screenshots from the App Store.
Another clue: Google's banner is also displayed in Chrome and smart app banners are limited to Safari. Google should use the smart app banner for Safari and the custom banner for other browsers. Oh, and you should be able the dismiss the custom banner.