I haven't really watched many of the FitTV versions of Cathe's workouts, but, as you say, they are usually condensed for time. And there are breaks in the workout because of commercials that don't exist in the regular workout.
I'd say you can get a good workout (not quite the same benefits, because some things are missing) by doing the FitTV workouts, with some caveats:
Don't do the workouts right off the TV, but tape them. I did notice in PLB, for example (I think it was) that the warm-up is entirely missing! That's an important part of the workout, as it raises body temperature, increases your ROM, and can lessen chances of injury. If you tape the workout, you can be sure to get in your own warm-up.
Another reason for taping is dealing with the commercial breaks. While they might be fine for weight training, allowing you to recover a bit and get in some stretches, they have a more disruptive effect in cardio workouts. By taping, you can fast-forward through the commercials and shorten these disruptions.
Taping also allows you to pause and rewind. I often put longer breaks between sets and between body parts when I do weight workouts (especially in the pyramid workouts, PLB most especially, and in MM, where there is no break between body parts for a stretch). This allows me to adapt the workout to my body's recovery needs and to my goals (strength and growth more than endurance, which I get from cardio).
Again, I don't think you'll get exactly the same benefits from the FitTV versions, because there are some things missing, but definitely a good benefit, especially if you are newer to Cathe and/or weight training or step/kickboxing. The DVD's especially do offer the benefits of premixes, which are variations on the regular workout, some of which I actually prefer to the regular workout (I like doing the "all but core" premix of Bootcamp, followed by the "core only" premix, better than doing Bootcamp as-is, for example).
