On startup of JBossAS-6.0.0-SNAPSHOT I get two times this warning:
22:00:07,984 WARNING [FileConfigurationParser] AIO wasn't located on this platform, it will fall back to using pure Java NIO. If your platform is Linux, install LibAIO to enable the AIO journal
...
22:01:02,245 WARNING [FileConfigurationParser] AIO wasn't located on this platform, it will fall back to using pure Java NIO. If your platform is Linux, install LibAIO to enable the AIO journal

By evaluating the property os.name JBoss should find out if it's a Linux system or not and raise this warning only if it's a Linux system.
In my case the property os.name is SunOS so this warnings are not relevant in my understanding.