Movies are just one advantage to having a built in DVD drive.
For example, let's say you are on a plane. You need to give multiple clients an updated copy of a large amount of data which you are currently working on and constantly modifying. Total file space required is 5 GB and your clients are running a variety of windows and OS X.
With a DVD burner you burn the data to a half dozen compatible DVDs. You meet with the various clients, discuss your business, hand them the disk, and you're done. You get a raise for a job well done. You splurge and buy a blu-ray version of "Live.Free,Die,Hard" to enjoy on your flight home.
Without a DVD burner, you meet with the client, try to figure out how to get connected to their corporate wireless network which is protected with firewalls and special login accounts. You then try to figure out how to access your clients machine once you are on the network. Then you begin the painfully slow process of transferring the 5 GB of data files. You spend so much time with client one & two, that you barely have time to meet with client three. You don't meet with clients 4,5, & 6. Consequently you are fired because you are inept at meeting and supplying your clients with accurate data. You are so disgusted with the MBA that you toss it under the plane as you board!
Now don't you wish your light weight portable had a burner like the 3.4 lb. Sony Vaio Z?
Problem is, that you can't fit 5GB on a DVD