Depends on the field of study. There are, for instance, many sites with many thousands of whitepapers each for computer algorithms, genetics, and many other subjects (I've looked into those two, otherwise I'd list more). A single site can eclipse several large libraries for that kind of information.
Or, in a more specific case, try looking for 3D rendering techniques. Info on the internet easily encompasses and eclipses all printed info on the subject, and it's significantly more up-to-date in many cases.
In a more general case though, yes, I agree that many studies would fall short if done exclusively online.
I completely agree that it was by no means a perfect source of information, but when you're at a school level and doing seven different subjects it was the most practical and possibly appropriate, as long as one looked beyond just Wikipedia.
Possibly not the best for teaching research skills with books - but it did help with learning to sift through a lot of information, which I'd argue is more useful that having your school assignment 100% correct.
Were all the Internet sources you used reliable and documented? And how could these sources possibly duplicate the knowledge found in printed books, considering most books still aren't digitized or freely available to browse online?