Yip. Same reason for the 'mat' lining the bottom of the body of the car. It is effective. For the rear, it also has the side-effect of limiting the amount of car-melt (a.k.a. road-salt) that reaches the upper regions of the strut tower or wheel well body. The liners are also light-weight and easily replaced. Sound-deadening material sprayed onto my previous car, which was normal practice back then, was not only much less effective for deadening sound, but also had the side-effect of sealing in moisture and hiding the rust.
I didn't much like the idea initially, but obviously it has grown on me.