How does Arsene do it?

Wenger is an excellent manager, he doesn't need debt to build a great team. Two reasons why Arsenal keep him on. As you said Chelski, MU and now MC have needed debt to try to buy trophies, yet Arsenal still produce excellent young teams. I hope in a few years, or longer if he stays, whoever succeeds Wenger will maintain his style of play and management. The Arsenal board is also to thank for the club's stability and paying down debt for the new stadium, during a recession!