At the announcement it was couched as "Exchange for the rest of us" – it was trying to outdo a competitor's product. (To say nothing for how it countered many of the features Google was trumpeting for Android…)
SJ was absolutely aware of MobileMe, and was intimately involved with many parts of the product.
And, given all of that, it still was a flop of a launch. A launch that was so bad, I'm sure it was a motivating factor in the iCloud rebranding.
And to claim the G4 Cube was a minor product is just amusing. SJ was incredibly proud of that machine when he announced it. And you know he was deeply involved in its design, from day one.