back in college the first problem set in my intro AI class was something very similar to this, except instead of maximizing the points scored on the current throw, it looked ahead and solved for the best "path" to get to zero points given your current score (in darts you win by reducing your score down to zero). Like the OP, I also remember being surprised by the fact that the bullseye wasn't the highest scoring point on the dartboard, but things get even more interesting when you look at the optimal strategy for actually winning the game.