As far as I know, yes, that's right. With regular MIDI, it's just sending the data across, no power, and it's very simple, so anyone with a bit of engineering knowledge can make a MIDI client or server. This means there's a wealth of both, with a lot of devices doing both at once. Which is nice.

With USB, it's a great unified solution to a lot of peripheral problems (as anyone who remembers serial and parallel ports can attest to, let alone SCSI) but that means having this rigid adherence to a master/slave dynamic, and it being too complex behind the scenes for most people to implement the master side of it.

So a regular non-USB MIDI keyboard should plug into it just fine, but you'll also need to plug it into something else to power it, as you say.

If it's any consolation, if you plug a keyboard and the Doepfer into a computer, there really isn't any noticeable delay. The tech's so fast these days, there's probably a bigger delay now between the speakers and your ears, given the speed of sound and all. :)

All the best,
Zoë.