The life of any composite structure (arrows included) is dependant on the quality of the fiber used, the resin system used, the surface finish, the number of cycles (shots taken), environment the arrows see during their life and what the arrows experience during use:
Fiber - There are many grades of graphite fiber. The higher the grade the higher the strength and durability.
Resin - There are also many different resin systems. Some have super bonding properties but are brittle when cured, others are middle of the road but flexible and can tolerate a broad range of temperatures (no doubt the ones used for arrows).
Surface Finish - The smoother the arrow is the less likely to catch things and cause even tiny surface scratches - these eventually turn into cracks that kill the arrow.
Cycles - Each shot loads the arrow in either compression or tension (depends on which side of the arrow we're talking about)for a short time. The quality of the materials used and manufacture will have a lot to do with arrow life.
Environment - Use during cold weather or extensive exposure to bright sunshine will greatly effect the life of an arrow. During cold weather every resin system is more brittle - arrows are more likely to develop small surface cracks during clod weather use. Sunshine exposure over a long time can break down the fiber/resin bond and reduce an arrows overall strength.
Arrow use - If you really work on extending the distance you can accurately shoot at or you shoot 3D shoots where you sometimes miss the target you greatly increase the possibility for damaging a graphite arrow which will eventually and sometimes quickly end the arrows life.
I think you pretty much get what you pay for. The more expensive arrows are usually straighter and use higher quality materials. I use Gold Tips which aren't close to the top of the line but they work fine for me.