Not a lot different, really.
Well, as it turns out, with evolution being what it is, animals being descended from earlier kinds of animal; it should come as no surprise that the anatomy is going to be relatively familiar across species.
The images shown here demonstrate that even between amphibians and mammals, there's quite a lot of similarity --- the musculature comprises homologous structures. You can clearly see the pectorals, rectus abdomini (six/eight pack), the external obliques.
As for the motivations of fantasy artists, I've noticed that, anatomically speaking, when it comes to werefolk of one kind or another, artists tend to plop a cat or dog head onto a human body, cover it with fur, give it an anatomically incorrect tail and call it a day. They don't make tiger people's bodies look very tigerlike! I think the reasons for this are twofold: first, trying to figure out what a feline body will look like after millions of years of evolution into an upright posture is no easy task. Bones will lengthen and change shape; joints will move differently; muscles will alter their place and function. The resulting body might look something like a human body -- maybe thinner and more flexible -- but its shape will be quite different even though the underlying muscles will all have human homologues.
The second reason is boobs. Yep. Whenever we see a Werecat or Werewolf or Werewhatever female character in fantasy, what do we see? Wide human hips and big human boobs high up on the chest. If you've ever owned a girl cat or dog, you know that wide hips and high boobs are not a thing among most animals. I suspect that a real Werecat would retain a relatively narrow pelvic girdle and six or eight tits along the abdomen. Not very sexy for movies, but, that's reality check!
Here's a cat:
Here's a dog:
Here's a frog: