See here:
Microsoft: Windows Phone 8.1 Preview for Developer users should return to normal software before Lumia Cyan | Windows Phone Central
The issue won't affect HTC users but I'm assuming they've halted it completely for the time being for all users (as that's easier to do).
"We are currently investigating the issue. We have paused delivery of the update to customers using the Preview for Developers, and will resume once a fix is in place. Customers whose phones have been affected should use the Nokia Software Recovery Tool to return your Lumia to a normal commercial software state before downloading the Lumia Cyan update."
Which also means no Preview updates at all, so you probably can't even grab it initially until the re-enable it.