kathryn
Cathlete
I don't think you were off in thinking that DVD production may play a roll in it. Producers pay for time, there is a certain expected 'flow' to workouts (that are usually done with shorter rests than one would use in a gym, or which might be ideal) and any fitness DVD producer who strays too much from the typical 'flow' might lose some customers. These are production issues.
Also, home users probably don't want much 'dead time' in their workouts even if that 'dead time' is a beneficial rest (it can seem like 'paying for a screenful of nothing'), and maybe more would complain about there being 'too long' breaks than if there are 'too short' breaks*. At the same time, the home user can pause or fast-forward, so if a rest period is too shot/long, it can be changed.
*Even I, who value my longer recovery periods, am a bit annoyed about Tony Horton's first one-on-one DVD, where the breaks are 'too long' IMO (he's just recovering from a cold---great time to film a workout?--and that factors in), especially since there is no chaptering, so 'chaptering forward' isn't an option. (And pausing to create a longer break would be easier than FFing to 'just the right spot' to create a shorter break).