http://forums.obsidian.net/topic/67500-more-obvious-xp-notice/?p=1486643
Alright folks, well, this certainly answers that: The quest-only xp system is intended this way (perhaps with some long quest being divided into one or two xp chunks before the final xp lump)! So, no mistake, this is what they meant by objective/challenge xp, it seems. I'll be darned.
Man that is disappointing to read.