Apple has the iPad and iPad Air. Not to mention the iPad Pro lineup. My iPad Air is noticeably lighter than my wife's regular iPad. The difference in the nomenclature is the weight of the device. Some marketing gimmick that the device feels lighter than Air. Yeh, right. Having multiple product lines is not unusual.It's not an Air because of it's absolute weight
I think Apple will continue the designations. A light(er) device such as the Air will appeal to many people that are light users. Especially those that travel. Yes, a pound or two is not much, but it does get noticeable the more one travels. The regular MacBook will appeal to users that need more function, external displays or more processing power.
Personally, I want the smaller screen, 13" over a 15". Easier to fit on an airline tray, easier to carry as it is much less bulky.