The thing you have to understand about these large online sites is that most of the time when you call, you're talking to someone: 1) who works in a call center; 2) has worked there less than 6 months; 3) is not a certified travel agent; 4) has never even been on a cruise; and 5) basically knows nothing about cruising - they're just there to sell you something.
Anybody can sell you a cruise. But it always best to seek out a reputable agent who is conscientious and wants to provide you good service before, during, and after the sell. Their service can be invaluable, especially if you have alot of questions or run into any problems. They are there when you need them.
Alot of online sites are betting that many people will just book their cruises electronically and don't need any personal attention. If you don't have any problems or need any assistance, it can work well. But personally, I'd rather be able to pick up the phone and talk to someone who cares about me as a person and has the knowledge and experience to assist me than to be treated like just another number.
Yes, there are exceptions to every rule and occasionally you'll find someone at the cruise line or an online site who is very good. But the fact of the matter is they won't be there that long because it's been proven the average lifespan of these call center employees is less than 6 months. They take the job thinking it's glamorous with good pay and great travel opportunities. It doesn't take long for them to realize it's alot of hard work, the pay is not that good, and the amenities are no where near as good as they thought.