Comixology has just announced that they are discontinuing their dedicated comic reading app for Windows 8. Instead, the company is encouraging their users to use their internet browser and read comics online.
It is very likely that Comixology noticed that hardly anyone was using the Microsoft Store and using their dedicated app for Windows. Keeping the app regularly updated, when a very low percentage of people actually used it is like throwing money away.
Nothing will happen to the comics you have purchased if you are an existing Windows user. All of the content is stored on your account, so you can simply use their website or myriad of apps for Android or iOS.
In order to make this transition as smooth as possible, Comixology is automatically adding $5.00 in free credit to your account if you had purchased at least one comic using the Windows 8 e-reading app.