Whats going on with this?

From:  "Jason Hopkins"

Why does Goofy stand erect while Pluto remains on all fours?

TB researched this: 

75 years ago when Mickey Mouse started out, pluto was just background filler for Mickey. Later as Disney's cartoons became more popular other characters came into being and to give them a more than a 2 dimensional character, they were personified and fleshed out to make them more interesting and have a more flexible storyline. Goofy came later after Pluto was defined.

Sarah-J simply answered this: 

pluto is just a pup. and goofy is...well...goofy's goofy.