I found this in my dashboard once I added “send trackbacks” under “screen options” from the “edit post” page:
“Trackbacks are a way to notify legacy blog systems that you’ve linked to them. If you link other WordPress sites they’ll be notified automatically using pingbacks, no other action necessary.”
It is the reference to "legacy" systems, and the fact that pingbacks are given automatic status over trackbacks that leads me to ask if trackbacks have been deprecated in favor of pingbacks. I seem to recall getting trackbacks automatically even from another link within my wordpress site maybe six months ago, in 3.1.
I understand that trackbacks are more at risk for spam, and maybe that's the reason for the change. I just haven't seen any more discussion about it than this note I referenced. Thanks for filling me in.