I think we're talking about two different things here. I'm not talking about the regular Bitlocker encryption that has been around since Vista for Business customers. I'm talking about the brand new feature called "device encryption" which comes with Windows 8.1, is obviously based on Bitlocker, and encrypts hard drives of supported devices by default. However, for it to work one must use a Microsoft account since the recovery key is stored on Microsoft's servers. Other than the regular Pro/Enterprise Bitlocker device encryption does not allow you to save the recovery key on a thumb drive or anywhere else (except for Active Directory environments but who has a fully operational Windows Server 2012 domain controller at home?). I found an excellent blog post explaining device encryption in detail on internals.io:
http://internals.io/blog/2015/4/14/w...ice-encryption
That said I can enable device encryption in PC settings on my Transformerbook. However, after enabling it I only see the internal 32GB eMMC SSD encrypted (or, to be more precise, I see that it's ready for encryption and will get fully encrypted as soon as I switch from a local to a Microsoft account) but not the additional drive that sits in the Transformerbook's keyboard dock and I'm wondering what the catch is here. I don't see a way to enable encryption on that additional drive as well, and it doesn't seem to get encrypted be default.