There's only 2 responses so far, take a breath
<--edit: that was before Rat & Cynthetiq beat me to it...
At the same time, to use your bus-analogy: If I buy my bus-tickets beforehand I pay 1e20 for a ticket, if I pay it on the bus, it costs me 1e60. If I get a pass, it costs me .80c
And get this, all for the same kind of seat!
Saying you expect 30e more in value if you payed 30e more, doesn't even fly in case of a bus, why would it for a plane?
At the last moment, the availability of free seats goes down, and so the price tends to go up.