That's the gist. Or, like I said:

DBU is good for a text based dialog (buttons and labels)

Pixels is good for a graphics based dialog (icon objects)

Some people use Pixels because they use pixel math for resizing and moving, and don't know about $dbuh and $dbuw and the extra effort involved in converting these values.

Well. At least I won lunch.
Good philosophy, see good in bad, I like!