Simply put, it's easier to do. Pushing up on the control stick is much easier than finding that right angle forward/up. But this is coming from someone who doesn't practice it...at all.
Which thread are you refering to? I remember getting a six frame advantage myself. But I could look into it again.
On the Wario thing, I explained this in my video:
http://www.youtube.com/watch?v=G2g8RjlgMwQ (the explanation is in the video description)
The first example you gave, just how often does that actually happen. If you're going to be punishing someone who is trying to land without a jump...for one, they're going to be air dodging anyway...and two, why punish with a single jab when you can do other things just as easily(grab, smash, tilt, etc.). The positioning argument is somewhat more viable, but...eh, doesn't seem all that useful to me still.
Listen to what Bored said.
EDIT: Found what I did on the 1st Jab from like...7 months ago.