Well it doesn't come with Windows 7 by default either. It's just one of those things that everyone has to install whenever they reinstall windows. I also don't believe it comes with snow leopard either -- maybe the only change was remove the option of installing 3rd party plugins in Safari.
See the link[1] and thread[2] about Flash-less MBAs.
[1] http://www.engadget.com/2010/10/20/macbook-air-all-substance...
[2] http://news.ycombinator.com/item?id=1814713