yeah, I've learned with motorcycles that valves do indeed need adjustment every so often. The nature of the samurai motor though explains the longer intervals. lower rpms are FAR less abusive on the valve seats and such than the GSXR600, or kawasaki ninja 500, where your NORMAL rpms are around 6-10k, if not 15k on the GSXR motor.
All valves tighten with time though, as the motor runs and the valves and seats wear, they tighten up, necessitating the adjustments from time to time.