LOL. Actually, it might just be in India! Rupees, yes yes. ^^
It is possible to explain the change in Rupee value as inflation/deflation, but I'm not sure it's that uniform. I'm too lazy to check (-hopes the mods don't kill her-), but I think that in some games there are rupees that have increased values from other games while also having rupees with decreased value. An explanation could be that 'rupees' are just a kind of gem, and the different colours have different values which can fluctuate independent from each other.
Examples please. I though most prices of things like bombs and arrows were pretty stable throughout the games, but you have to remember that different merchants hav different prices even in the same game (LoZ being the prime example).
As far as I know blue and red rupees have had the same value of 5 and 20 green rupees respectively in every game they have appeared in, so at least the base denominations seem to be standard throughout Hyrule's history.
I agree with its placement. It presents an observation -- that the value of rupees is not uniform throughout all of the games -- and then proposes a reason why. Essentially, the question could be presented: are rupees created or naturally occurring? Either way, something is happening to cause a fluctuation in value (even if not every single rupee colour fluctuates.)
I would say simple supply and demand cause prices in hyrule to rise and fall. Also competition/price wars between merchants will drive down prices while a lone merchant in an isolated area will charge more.
I would also go so far as to say that rupees are mined/cut by the Minish or dwarves or even the gorons, with small green rupees being the most commonly found underground.