I completed my entire undergrad online through FHSU (Go TIGERS!) and for the most part my experience was quite good.. yes, there were a couple of professors who failed to communicate with the students, but most were quite good. If extra help was sought, they were willing to help through email and BB forum discussions.
What weighed in my favor was that I was in my mid 30s when I started it - I had the self discipline to study at home while working FT and make the Dean's List. I loathed classes where group assignments / discussions were mandatory as more often than not people would "contribute" their part of a discussion topic with mere minutes to spare before the deadline: One can not have a discussion without user interaction.
It can be done, but success is entirely dependent on the person - and what their motivation is. Perhaps HS simply does not properly prepare for College; perhaps time management issues quickly become evident when no one chases you down to complete assignments.. or perhaps the thinking is that online college courses are a joke and easy.. and they find out that it isn't so... whatever the reason, whether one completes a degree or not is up to the individual and one shouldn't blame the method of delivery.