> If your t.v. has an HDMI port it more than likely has a USB as well.

This is probably true for current new TVs, but HDMI ports were common on HDTVs before USB ports were, and not everyone replaces their TV every year.

Actually, many (perhaps even most) TV USB ports don't provide power (or good enough quality power) for anything beyond basic thumb drives. It's also possible for ports not to offer power unless the right handshake is made by the device. Also, some TVs have a USB port which is only for diagnostic use, and can provide unsteady/harmful power output.

However, I'm guessing this device ships with a USB cable + wall wart for everyone else.

It does....

Neither of my TVs have USB, but both have HDMI. I'd hazard a guess that the older "brand new HD" TVs that came with HDMI first will need external power, while modern ones won't need it.