Imagine if Pelihu or Rustmonster went for a joint MD/MBA? With a JD already under their belts, they'd be vying for the "King of the Universe" spot.
If I told my wife I was thinking of getting an MD after business school, I'd probably be a bachelor again real soon. :D My (now) former law partner was a neurosurgeon before going to law school, so he obviously has an MD and a JD. He's just two years away from the Trifecta!
More on point, he says law school was much harder than med school. To him, med school was just power memorization, whereas law school was more intellectually challenging. Ive got friends who describe law school as "intellectual boot camp" - there's truth there. He also commented on the MCAT v. the LSAT, arguing the LSAT was intellectually more challenging but the MCAT was harder to prepare for because it tests acquired knowledge. In that vein it shares something in common with the bar exam and medical boards. That is, of course, just one opinion.