That is true. However, it is not really a problem in the long run unless every last bitcoin is lost. You can divide bitcoin in infinity and trade with micro-bitcoins or pico-botcoins instead. So at first though this seems like an issue but I argue it isn't.
You can't divide it infinitely. The smallest unit ("satoshi") is 10^-8 bitcoins, so in total, there will only be 2.1*10^15 units of money. For reference, the total M1 money supply in the world is equivalent to about $25 trillion, or 2.5*10^15 dollar cents. If bitcoin becomes a major world currency and we assume a currency loss rate of couple of percent per year, it's gonna become a problem within couple of decades.
There could of course be a change in the protocol so that let's say any bitcoins not used in 50 years could be remined. But it's something that requires acceptance from majority of miners.