I've always based this argument on how the instrument sounds rather than what features it can offer. Every TOTL keyboard is more than adequate to be played in a live / pro situation and it wouldn't sound out of place.

I was reading some of the history pages on various manufacturers sites and this quote totally backs up my own beliefs that it's primarily in the sound:

"Korg introduced its first professional arranger in 1993 with the i3 model, which proved to be the first in a huge series of Korg 'interactive' products. Until that time the auto-accompaniment keyboards were designed primarily for home use, but i3 changed that. Its tone generator was an AI2 engine coming from the renowned Korg synths, which made it a perfectly useable 'pro' keyboard."

Danny.