Yes, they absolutely do. It would completely murder the supply chains to have such massive droughts in demand, and it would be extremely hardcore fucking over customers who had to have a phone in the period near the end of those terrible cycles by immediately making their phones obsolete.

If Tim Cook announced tomorrow that he had a proven cure for cancer and that he was also cutting the phone cadence from one year to five, he should be fired the same day. Annual updates are the only valid approach.