I dont see ducking, or slipping in the other direction used half as much. Nor do I see rotation or bending at the legs for slipping as much as youd expect, theres ALOT of bending at the waist only. I mean even Perry Whittiker who is a southpaw (who shouldnt use this slip as much) and the best defensive boxer ever (perhaps) avoids right crosses by bending forward at the waist when he is "meant" to be slipping the other way to avoid right crosses and he is meant to bend at the legs not the waist. Is it wise to do that to avoid a southpaws left cross? In case you are wondering what slip I mean, I mean the slip to the right you are an orthadox fighter. (or to the left of you are southpaw)
I've seen Pea slipped correctly, and slip with a straight drinking bird duck. I think it's just the variety of moves a guy has.
In general I have to agree with the thread starter, though. Feels like it's quite rare to se fighters rolling, by just bending at the knees, under hooks like taught in the gym. It seems to be more common to bend primarily at the waist when ducking. Is it since there's just no time to roll properly under hooks from pros, especially when the opponent is shorter? Slipping outside right hands in the correct manner isn't as common either, but since it's often overhand rights being thrown I suppose it's hard to do.
I'd say it may have to do with the fear of if they say slip the the right and at that moment the fighter throws a right hook instead of a straight you are probably getting Ko'd. Bending at the waist or bending back eliminates that fear even though you are still most likely getting hit albeit less cleanly.