Microsoft halts Windows Phone 8.1 Update 1 Developer Preview for HTC models12
So why are those two HTC phones unable to install Windows Phone 8.1 Update 1? According to Microsoft, it has to do with a driver update that each of those HTC phones need. That update has to come from the manufacturer, before the Developer Preview version of the update can be sent out to the two models.
We understand that the HTC Windows Phone 8X and HTC Windows Phone 8S do not represent a large percentage of the Windows Phone market. The HTC 8X had a 4.7% slice of the U.S. Windows Phone pie on July 24th, according to AdDuplex. But that doesn't mean that owners of the two models should be denied the opportunity to install the latest OS build, even if it is a via a Developer Preview.
source: Microsoft via WPCentral