Response from Griffin below. If enough people contact them and request current driver support for the USB Powermate, and/or Windows drivers for the new BT PowerMate, they'll apparently make it happen. I don't think Griffin considers how many sales are lost because of the obviously ancient drivers for the USB PowerMate. I also don't think they're taking into account how many Mac users also run Bootcamp (Windows) on their machines. A lot of Windows developers actually buy high end MacBooks and toss Bootcamp/Windows VMs on them as opposed to buying Windows hardware, so they are in particular a market that will likely pass on a Mac only PowerMate.
These days I'm predominantly a Windows/Android user (Apple does a lousy job of supporting gamers with their hardware, which ultimately cost them my business), but I have a four year-old 27"iMac and a two year-old MacBook Air, and the ability for my Mac accessories to also work in Bootcamp has always been important to me. Speaking from personal experience, buying an accessory that becomes a paperweight when you swap over to Bootcamp is less than desirable, to the point that I, for one, will skip the purchase.
I'm tempted to start a Change.org petition or something....
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Thank you for the email and your interest in Griffin products.
1. The Powermate bluetooth is not currently slated to be compatible with windows based computers and will only work with those Macs that have Bluetooth 4.0 or higher.
2. There are no current plans to update the drivers for the existing powermate to be compatible with Windows 8.
On both fronts, a compatible versions for windows is possible and I will definitely pass your feedback along
Sorry I didn't have better news
Jitin
Griffin Technology
Customer Support