The stats themselves don't change
...but the effective stats will.
I think you're confusing the spell's flavor text (which describes the reality in the fiction) with the mechanical effects that the spell specifies elsewhere.
Following from Polymorph Any Object, which says it functions like Greater Polymorph, which says it functions like Beast Shape IV, we finally come to just what the mechanics say.
Huge Animal - If the form you take is that of a Huge animal, you gain a +6 size bonus to your Strength, a -4 penalty to your Dexterity, and a +6 natural armor bonus.
Note that this is not a complete "replace your stats with the new form's stats", it is a bonus modifier applied to your original stats.