It's what it takes. A few other SF types, some better matches than others:
Dunleavy - 8.2
Turkoglu - 6.4
Hapring - 6.0
Brian Cardenal - 5.8
Battier - 5.8
Lakers who are being paid more:
Kobe - 19.5
Odom - 13.5
Kwame - 9.1
Radmanovic - 5.6
I think the salaries of the 2 in front of him are far more outrageous than what Luke will be pulling down, though Kwame got his for being the top pick (along with being very tall.)
More NBA salary info here.
Freakin' Brian Cardenal makes that much?