Where I think that the confusion may lie:
On a DVD, there is a hierarchy that (overly simplified) goes something like:
A Video DVD contains one or more Titles
A Title contains one or more Chapters
And from observation: Most "normal" Studio DVDs with a menu at the beginning are one title, regardless of the number of chapters.
Some Studio DVDs do have more than one title (at least, this is the way it was in earlier versions of Studio). The title breaks tend to occur when a menu is NOT the first thing in the list. For example (under earlier versions of Studio, anyway), if you had a DVD composed of a lead-in clip, a menu, and the remainder of the DVD video, you could have 2 titles -- one for the lead-in video, one for everything else.
So, in short, the whole TITLE being imported as one-big file regardless of the number of CHAPTERS? That's normal behavior.
BittMann