Of course, there are other criteria for rationality besides coherence/consistency (as the wikipedia article alludes to).
According to criteria that would label hyperbolic discounting irrational or illogical, debt collectors are equally confused for not accepting the promise of a $100,000 payoff 50 years from now rather than a settling of the debt today.
In the real world, you have to deal with the uncertain risk that the offer will be unfulfilled due to external factors, which always increases in time relative to present. You, the entity offering you the choice, or the entire environment both exist in, may not still exist in 60 months.
If the same offer is made 60 months from now, you should make a different choice, because the risk of non-existence between time of choice and time of reward has changed.
If the amount of hyperbolic discounting is genetically determined, then is likely that we are still adjusting to the massive drop in risk of death over the past several centuries.
Seriously though, I thought we already knew that human perception is mostly logarithmic (for example, the eye performs well across 9 magnitudes of brightness – a linear system doesn't make sense). On the other hand, human perception of future value has generally found to be discounted hyperbolically, which is illogical (http://en.wikipedia.org/wiki/Hyperbolic_discounting).
I wonder is there is a correspondence with the harmonic mean but I can't get my head around it at the moment.