They really do sound that different. Same mic positioning. The challenge with positioning is that the top speakers are angled being that this is a slant cab, even though the overhang makes it look like a straight cab. I got a really good deal on this cabinet a few years ago, I bought it off my friend Jeff Kendrick from Devildriver because it's a fairly beat up cabinet and he got a Mesa endorsement and new cabs at that point.
In spite of that, I found that each speaker has its own unique tone to it and was worth capturing as an impulse. Move a microphone even 1 millimeter on the SAME speaker and the tone can change noticeably, so it's fairly understandable that 4 speakers can sound this different.
And yes, it's all Celestion v30s in this cabinet.