To answer your title question--Student do NOT need books, they just need quality resources.
The best option for this will vary depending on the subject, class size and teaching style (the latter more than the former), and the students' learning ability. For example, in a undergrad intro course filled with students of average ability, a standard textbook may be the best option, perhaps supplemented with a few additional resources (links to videos, papers, etc). However, when you are teaching an advanced course, with students who both know how to learn on their own and have some experience with the subject matter, a textbook may still be a good option (depending on your institution's policy, you may be required to assign on for the course), but students will learn more and better if you provide them with primary sources, seminal papers in the field, and thought-provoking position papers, in addition to the textbook.
As for which a lecturer should do,
write a traditional book or editable lecture notes
that will depend on all the above factors, as well as individual talent and motivation. Not all faculty members will necesarily want to write a textbook, though almost all will write lecture ntoes.