It also allows for the possibility of selling at discounted rates for volume. $1 for 4 tokens, but $10 gets you 50 instead of 40.

There is _some_ inherent value in this. Decoupling the currency rate from a unit of time play provides an entrypoint for the store to incorporate value models that aren't captured by currency alone.

In the volume discount case, this allows them to incorporate fixed overhead models into the pricing scheme for game time.

I don't dispute the point, however, that the model does allow for abuse along other lines, and is often used that way in practice.