Err... isn't any flight that gets oversold "popular" pretty much by definition?

I think simply put they use historical data, data on the tickets sold (and pax) etc. to forecast how many no-shows or ticket changes/cancellations are likely and calculate how many tickets to sell to maximize revenue while trying to avoid too many IDB:s. I could imagine they don't even limit the analysis on the tickets types, but also on are you traveling alone/ w/ partner/ as a family etc.
But anyway if they do their stuff right, the chance of the initially overbooked flight being overbooked at the gate should be about constant and not greatly affect you, as they've taken already these factors into account.

BTW, speaking of OP-UPs on sold out flights, I witnessed a OP-Down on a KF (DC) flight TMP-ARN last week... the plane was full and one guy was downgraded from Premium to cattle (with compensation). The weird thing was there were only 3 rows Premium in the Saab 2000, which is nowhere near the max. I've seen. Wouldn't it be cheaper (and better PR) for them to upgrade 3 guys (given they even sell those upgrades for mere 25€, none available for this flight though) than downgrade one? Does this happen often, or was there just a problem with catering or something?