It wouldn't be lighter because of PR.
Imagine the macbook (cheap) being lighter than the expensive MacBook Air whose purpose is being light. Basically undermining the point of the MBA, then try and sell the MBA for £250 more then the top end MB.
I can see getting rid of the optical drive but getting rid of USB, Mini DVI, headphone port would (I believe) destroy the student market for the Macbook. If you keep those available ports then what are you left with, the MBA.
Also note the url of the website ends with MacBook and note that the apple urls on their site are lower case.
I was working on the assumption (valid or otherwise) that this was real, although since Samsung have already used the tagline I doubt it: http://www.samsung.com/global/experience/ifa2008/ifapress/html/popup_notepc01.html. If it were I'm sure that Apple would find a way to make the MBA more desirable, or there is the possibility that the MBA will be scrapped and this will make the line wholly consumer orientated.