In the early years, AppleCare did not cover accidental damage and was only $69. Apple stated on financial earnings calls that the goal was to mostly break even. We were told as Apple technicians that we could replace an iPhone THREE times before it put Apple into red ink.
Over time the phones got more expensive to make/repair, especially the OLED screens, and Apple added accidental coverage, while lowering the deductible. They also run the division for a profit now, instead of break even.
AppleCare revenue covers all the phone support people, but also the Genius Bar/technician aspect of the retail stores, from an accounting perspective.
Edit: One more thing, AppleCare revenue belongs within the "services" division for accounting, which is the fastest growing part of the company. It needs to keep growing.