Replying to Ski Dimensions and "recommended use"

Ok, so all skis have different dimensions, and when I look at a ski's recommended use I generally look at the width at the waist.  I would generally think that park skis would be under 85, all mountain would be between 85 and 98ish, and pow would be anything above 100.  Is this the right spec to go by?  If so, then why are some skis like the line anthems at 93 a "park" ski, and salomon foils at 87 a "pow" ski, and blends at "90" an all mountain ski (according to manufacturers)? Is this just due to different flex patterns and constructions, or can you not really gauge a ski's use by looking at it's width?