I think it's due to some of the suppliers using Smartphone as a generic term to include both WM PocketPC and WM Smartphone, exacerbated by MS now using the WM6 Pro/Standard/Classic names.
I downloaded the free version to my O2 Zest and once I got used to it, it certainly makes the phone okay to use without the plastic stick! I only use the 5 keyboard part as this can be used with my fingers which was the whole reason for downloading. Integrates well and its easy enough to switch to the original qwerty keyboard.