I was looking at this thread yesterday because I also use iDVD extensively and decided to do some searching on the Apple website. It appears they're wanting to concentrate on iMovie (new "movie trailers" feature plus new themes) and FCP X which hasn't proven to be a big hit so far. And, since they've built in "share" to pretty much everywhere (Facebook, etc, etc) from both iPhoto and iMovie, I guess they think it's time to ditch iDVD.
May I suggest that anyone using iDV D send some feedback about keeping it:
http://www.apple.com/feedback/idvd.html
As for saving on a DVD, I don't believe that has anything to do with it; I believe it is Apple's idea to move us away from physical media and become MAS and "iCloud dependent". No install media, no external backups - only digital downloads and iCloud storage/backup. I'll stick with my LaCie's and SL if necessary (fortunately I have a fully functioning SL clone).