I don't think any of the models sampled one full octave and then resampled that for the other octaves. When you change the pitch of a recorded piano note through resampling, it's going to sound very artificial if you go beyond a couple of semitones. Typically you spread the samples out so you have 3, 4 or 6 per octave.

Also, most electric pianos support transposing the whole keyboard, which means that even when you just have four or five physical octaves, you can play notes lower than or higher than that. So that explanation for the price difference is not very realistic.