Yes, it has been troubling me, because I don't really have much of a clue about how that would affect the market other than to force it up. But by how much? Twice the rate? I don't know. For the sake of having numbers to look at that's what I have plugged in, but I have a feeling it could be a lot higher.
I expect that in 2 years, yield from transactions fees will be much higher. This should mitigate some of the disruption caused by the reward decrease.
If txfees are on average 0.001BTC and there are 100,000 transactions every block, that's 100BTC just in txfees.
If there are sill no fees being paid in 2 years then I would worry about the viability of the txfee market and that of bitcoin.