I think this is logical, no? Thrown a spear you surprize the enemy(so the enemy have not the time going in a defense posture ...) and so doing more damage. Plus: a "thrown" gives more power to the impact of the attack, no?
On 7th of february 2015 : I start a new adventure in the Divinity world of Original Sin, it's a Fantastic Freaking Fabulous Funny ... it's my All Time Favorite One !