Ghengis. I took that to heart from your, and others posts I had read here. When I went to speak to Exodus about it, they actually said exactly the same. They would rather people pay on a per lesson basis, and as such, they offer a minimal discount for paying up front.
Their logic was that paying a large sum sets expectations of lessons, and ends up with the pupil feeling cheated when lessons are cancelled due to bad weather etc. Paying on a per lesson basis keeps the interest and engagement.
Funnily enough, I had the opposite experience to Zeddie this week just gone. I got to the airfield for my lesson, and the weather was marginal. The instructor offered me the option of cancelling, or going through the pre-flight briefing then, and seeing how the weather was when we had finished. We did the briefing, and the weather was still not up to much, so he said we'll cover the briefing again in summary before we fly this week.
I asked how much the lesson was since it was cut short, and he said "nothing. The briefing is part of the lesson."
Seems good to me. I get to cover the briefing twice, which gives me time for stuff to sink in this time, and then apply it next time, and no charge until we fly.
Fingers crossed that Thrusday stays fine enough for me to actually apply the stuff covered in the briefing!