Was this a cost-saving measure, or was it a deliberate decision not to centre the seat? I can't see why there should have been any presumption that the seat ought to be centred, as suggested by your post. The current arrangement means that the extra space is useable; it wouldn't have been if it was evenly distributed on either side. In addition, there couldn't have been the useful extra storage area to the right-hand side of the seat.

In any event, I don't think that the seat itself is any wider in the E seats. It's just that there is more space to the right of the seat.