The highest-grossing films of both 2009 (“Avatar”) and, to date, 2010 (“Alice in Wonderland”) both had wide 3-D releases, along with their 2-D counterparts. Are audiences really this nuts about 3-D? Or are they responding to other qualities in these particular films? In either case, Dreamworks Animation’s new “How to Train Your Dragon” is the latest to use the process, which doesn’t really add all that much to its many low-key pleasures.