Hmm, that's not entirely true. I can book A-B-C in one booking on Easyjet. I was surprised to find that out a while ago when I booked CGN-LGW-INV. The two flights are on one booking and the fares are simply added. I only get one-printout and one transaction on my credit card. Different than on all other low cost airlines that indeed force you to book step by step.