Macbook Air - announced January 2008. Netbook - well, okay, I'll give you that the Eee PC came out in October 2007 (Asus have always been the outlier in experimental PC form factors) - but other manufacturers weren't seriously playing in the netbook space before the Eee sales numbers came in, so I don't think you can say 'everybody' had legacy-free optical-driveless netbooks out before the MBA.

But more to the point, a netbook was optical-drive-free because you weren't expected to use it for more than just web browsing; you weren't going to need to load software onto it. The MBA was optical-drive free in spite of it being intended to be a fully-functional notebook computer. You would install software onto it over wi-fi. And you wouldn't need to rip CDs because you would buy all your music from the iTunes store. In 2008 that was still a bold idea.