Felix Lee:

funny that [Callie]  has heels and none of the males seem to wear shoes at

all.

Huh?
The only male kats I know of who don't wear shoes on a regular basis are
T-Bone and Razor, and any kats who sun themselves at Megkat Beach. 

An advantage of not having any footwear:  being able to climb vines quickly
and easily in an elevator shaft (cf. "Destructive Nature").