I think it depends on the school and the individual students. Some students are auditory learners and do better in class. Other students tend to learn visually or kinestheticly. Here is a great, free, website that has a questionnaire that will tell you how you learn: http://www.vark-learn.com/english/index.asp
I was almost entirelly read/write with some kinesthetic so I was good to go online.
I took a hybrid class - the lecture portion was online and the lab in class. It was ideal because you could also attend the in-class lecture whenever you wanted (taught by the exact same teacher with the exact same material). The idea was that to allow for attrition - the online students take up the seats left empty as the traditional students dropped (our school had high attrition rates). With the hybrid, another advantage was that you still had access to the teacher for 3 hours a week for lab, for any clarification you needed.
I had a young child at home so I was never able to attend a lecture. However, I spent the 3 hours a week I would have normally been in class reading my book and the lecture notes, in addition to
the number of hours you would normally spend studying - so yes, to get a good grade and to get everything you can out of it, you are going to put in a lot of time. What I did save was transportation time and cost.
I don't think taking it online is cheating yourself out of any knowledge -I got the highest grade in both I & II out of both the online and on campus students (not meant to be a brag but to demonstrate that taking it online does not mean skimping on knowledge). As I mentioned, I think it depends on the program and student's style of learning. I did decide not to take it over summer though (online or on-campus) because I would not retain as much if I had to learn it that fast - but again, that depends on the individual and their learning style.