I would be surprised if the post was seriously stuck - an aluminium post shouldn't fuse to a steel tube. I would guess it was the original post, in which case they are very prone to becoming bent in use. And if you force a bent post into a seat tube, it will tend to get stuck. But not what I would call seriously stuck. At £80, I would have thought it a risk worth taking.
The other drawback of the bike is that the P2s are plain-gauge and there's a big difference - 2.3lbs vs 1.8lbs really does show up in the ride quality.