I am not sure why it's there either, but I for one really like the look of it. You gotta commend ILM for blending CGI / model elements into shots featuring that distortion. Must have been a pain in the butt at the time.

Would be great if you could add these distortions to shots in AOTC and ROTS. I don't recall any of these shots in OT, but there are probably a boatload of them, as is the case with lots of 70's and 80's films. Star Trek: The Motion Picture is a prime example full of these distortions, almost to the point of being overbearing.