Much as Google and Motorola have been doing for a while, HTC has begun to offer some of its apps to the Google Play store. While they have done so for a while now, these apps are ones that so far have come preinstalled on HTC devices and required firmware updates when new versions were released. Already available is the HTC Keyboard app and the HTC Clock app has also turned up.
The advantage of offering apps through the Google Play store rather than as part of the firmware itself is that updates are much easier to push out. Updating a single app will not longer require a firmware update. Whenever HTC is ready to update an app, it will simply push the change up to Google Play, thereby bypassing the longer OTA process required by a full firmware update.
The HTC apps are only compatible with HTC devices. While you will see them in Google Play, you will not be able to install them unless you own a compatible HTC device.
Source : Google Play