If you happen to own a Nexus device, you have the easiest possible version of the individual system app update process, where, instead of an OTA update rollout process, an app that came pre-installed on the device is updated to add and improve functionality. That's only because everything that's in your /system/app partition is Google, so every other device, Samsung to Lenovo, must wait for an app to either be added to the Play Store, as more OEMs have been doing lately, or wait for an OTA to fix the issues you are facing. HTC has been great with moving its versions of the system apps to the Google Play Store, so updates happen like any other app. Today, another one, the mail app, was added to that list.
Since last fall, as memory serves, HTC has been slowly but surely adding a variety of its system and accessory-related apps to the Play Store to facilitate the update process for them. the most notable addition before this year's M9 launch was the Blinkfeed Launcher, the Taiwanese manufacturers take on a social-centric home-screen, much like Google Now is in the Google Now Launcher.
But with the release of the HTC One M9 earlier this year, and the companion accessory in the form of the Dot View case, HTC added still more apps. This time, HTC added apps that allowed your M9 to have a customizable illuminated pattern or sequence, even including the capability of running and playing a version of the classic game Brick Breaker, dubbed Dot Breaker obviously, just using your closed Dot View case and One M9. The company recently added its gallery and camera apps to the laundry list of Play-housed apps, allowing for quick fixes and additions in case something needs to be addressed or managed.
But, with the mail app now in the Play Store, HTC One M9, among other devices, owners can benefit from an update here and there, if HTC ever uses the now-quick process, because some OEMs never actually take advantage of the Play Store updatability that they give their apps. Ideally, if some new feature hits HTC's developers, like a little less square of a design language for the interface of their mail app, then the process will now be simpler.