e.g., YOU deluxe edition:
http://www.hmv.co.jp/product/detail/2700798
It says
Other: +DVD, Limited (First Edition) in the detail section, so I guess hmv treats this as 1 unit and DVD as a bonus part...
Probably... it's a long sleeve case, so avex actually put the cd and dvd at one single long cd case.. The regular press has the thick cd box again, so they treat the regular press as 2 units?