I too am surprised that more flyertalkers don't realize this; or maybe they just don't acknowledge it.

But there is a problem related to the OP's question. In my family there is a fixed amount of vacation time per year, and I've found that once we've picked a place, I can find points for tickets about 60% of the time, and buy tickets the rest. Recently I have been getting points at a faster rate, while spending them at the same rate. Thus the number is growing and the marginal value of the points is decreasing. If/when my job has me traveling less, the marginal value will go back up.