Gem prices may be that cheap now, but wait a few months. Every game I have seen where you could purchase the “premium” currency using ingame currency started out cheap too. Then the gold farmers get rolling and EVERYTHING skyrockets until the average player simply cannot afford to do business anymore without spending a fortune in real life cash. I understand that one of the very reasons the currency exchange exists is to COMBAT gold farmers. However, in my humble opinion, it doesn’t help.
The term buy low sell high is your friend in freemium games, and GW2 IS freemium, don’t let the initial buy in fool you. It is the ONLY way to compete with the gold farmers. Unless of course you want to spend hundreds(literally) of real life dollars, or hundreds of hours farming gold. BTW, I got my first ingame gold spam email today! I felt so proud!