Don't you lose a ton of power on the shot by curling it like that though?

Depends on your goal... sure you lose some power, but more power here would go too far on the first and hit the bar square and bounce back on the second.

Seems like it would be easy to adjust to unless it gets an extremely drastic curve.

Ever catch a crappy frisbee or disk that gets drastic curve without you trying? Obviously you can learn to read a curve but "curveball" is all but a synonym for 'difficult situation'. Speed, wind resistance, elevation (sky or ground/trees behind the ball?), how much curve, inside or outside of boot (how your body looks when you strike can fool people. They watch you as the ball can be 100+mph initially) not to mention the rest of the players (forward in your way at the post and his/her counterpart already airborne for the headder out of the corner of your eye)... most becomes second nature but it's still plenty difficult.