In an ideal world then I would also agree.
That said, if you're replacing a boiler like for like, not many customers will appreciate the additional cupboard space required in order to house a red beach ball in the kitchen cupboard below. Especially when the other products offered don't need it!
Are you saying the overall size of boiler has now increased on the rapid to house the expansion vessel?
My understanding was that they could wiggle it in to the existing case (which was the main reason for changing to a centred flue!)
If it's the existing case, then without the rear jig it makes it a nice compact and solid unit.