Originally Posted by
Zulandia
I haven't really been looking into the gems in D3 much, but going off D2 they work a lot like the gems in WoW, only opposed to having to buy new gems as you go (green > blue > epic > next expansion) you simply combine multiple of the smaller gems to make a higher tier one. lower tier gems will also drop while you play the game (if we believe the OP, the highest tier gem which will drop is 5) and then to reach the higher tier will require you "build" them. It should be noted he is assuming the prices of gems on the RMAH, they will also be able to be farmed to an extent or be bought with in game currency as well. He's trying to make a big deal out of a small thing more or less.
TL : DR if you choose to buy them instead of spend time to get them, much like anything convenience costs you.