This was the case in the early days of OSMF because the query string params were not being passed to the server in the NetConnection.connect() and NetStream.play() calls. So you needed to load the plugin to play secure streams over Akamai. However, OSMF now passes all query string params in these method calls so token authentication will work without the Akamai plugin loaded. The other thing the Akamai plugin does is issue FCSubscribe calls for live streams. However, now that the Akamai network has been upgraded to FMS 3.5+, those calls are no longer necessary, so live streams should play fine over Akamai without the plugin loaded.
The one thing you won't get without the plugin loaded is connection re-use for secure streams, since the key generation for identifying connections won't include the auth tokens if the plugin is not loaded.
The key thing the plugin provides for Akamai and it's customers is the ability to handle things that are specific to the Akamai network without affecting the core framework. So today, most things work without the plugin loaded, but this may not always be true moving forward.
I thought I would take a moment to update this thread since several months have passed since that last post.
There are now two Akamai plug-ins for OSMF:
1) The AkamaiBasicStreamingPlugin : this plug-in is open source and can be found in the OSMF source code repository and in the OSMF releases. It handles connection level and stream level authentication for FMS single and multi-bitrate streams (dynamic streaming) for both live and VOD. It also handles live connection retry if both primary and secondary encoders crash. All the metadata keys can be found in the plug-in's PluginInfo class.
2) The AkamaiAdvancedStreamingPlugin : this is a proprietary plugin that provides Akamai HD Network streaming and improved Zeri (Adobe HTTP streaming) in addition to everything the basic streaming plug-in provides.
If you are an Akamai customer and using an OSMF built player, you should be using one of these plugins. Which one depends on the type of media you need to play. Contact your Akamai sales rep for a copy of the Akamai plug-ins document. It contains detailed documentation about how to use these plug-ins and also contains several samples with source.