I think it's because I interact with boarding passes so infrequently that the data alone isn't enough for me to glean information – I need the explanation of what I'm looking at.
E.g., I know (555) 492-2882 (in the U.S.) is a phone number without it being labeled because I use phones enough to learn the format. I don't immediately know that Zone 5 is a seating schedule or a gate, because I don't fly enough.
I could see the design slowing down experienced fliers though (verbose UI tends to do that). It looks like the data is repeated in a just-the-facts style in the right column (maybe for that exact reason), but rather than repeating everything I think it'd be cool if the descriptive section was rearranged so the numbers all line up vertically or something for even easier scanning for those who know what the numbers mean.
I'm really impressed with that design solution though, and how JJ approached it differently from everyone else.