Most upperclassmen do own their own bassoon, but I guess some don't find it necessary to buy one when they can rent one. It is better to buy one as early as possible because every bassoon is different, even ones that are the same model, and if you get your whole education on the bassoon you are going to be using for the rest of your life (or at least early audition) you get of have a better feel of it and the tuning and resonance of your bassoon giving you a leg up in auditions. And Auditions now a days for symphonies are VERY competitive so you need any advantage you can get.