This paragraph varies with device. It's just a placeholder for a paragraph that should have revealed a lot of useful information. Unfortunately there are so many devices and they have different characteristics, so it's hard to write a paragraph that encompasses their complexity.
This screenshot varies with device. It should show some important information about the Google+ app for Android, but it doesn't because there are multiple Google+ APKs and each one is different.
On a more serious note, there are many Google Play apps that show the uninformative "varies with device". The size of the app varies with device, the current version varies with device and so is the required Android version. That's because Google Play allows developers to upload multiple APKs for the same app:
Multiple APK support is a feature on Google Play that allows you to publish different APKs for your application that are each targeted to different device configurations. Each APK is a complete and independent version of your application, but they share the same application listing on Google Play and must share the same package name and be signed with the same release key. Android applications usually run on most compatible devices with a single APK, by supplying alternative resources for different configurations (for example, different layouts for different screen sizes) and the Android system selects the appropriate resources for the device at runtime. In a few cases, however, a single APK is unable to support all device configurations, because alternative resources make the APK file too big (greater than 50MB) or other technical challenges prevent a single APK from working on all devices.
Even though Google doesn't encourage developers to use this feature, most Google apps use it: Google+, Google Chrome, Gmail, Google Maps, Google Search, Google Play Books, Google Play Movies & TV, Google Translate.
Since Google knows which devices are associated with your Google account, it could show a drop-down that lets you select one of your devices and show the appropriate information. For example, you have a Nexus 7 running Android 4.3 and a Galaxy S3 running Android 4.1. Select one of the devices and replace "varies with device" with something more useful.
AppBrain manages to show some useful information: