13" MBP speakers aren't exposed whereas the ipads is. So its likely that the ipad may seem better.
Actually, I also did a speakers compare with my Macbook and it was very close but the iPad does appear to be louder and have better frequency response. I don't know if thats psychological or if the iPad acoustic modeling is something they'll start pytting in macbooks and iMacs.
13" MBP speakers aren't exposed whereas the ipads is. So its likely that the ipad may seem better.