Something that don't make any sense to me is the purge memory option in File.

 Why do we need to go and clcik on it when it could be coded in to do this when memory needs purged.   Am I missing something somewhere.

Yeah, it is kind of complex, but the system has to know it is getting a purge as not to lose data. 

So, while you are waiting for the purge to take efect, the app is on standby.  Otherwise, if this purged occured silently in the background, and if the app and system were not on standby, you could lose data while purging and working on the app at the same time. 

The purge is not always successful, and sometimes it is better to save, shutdown Vue, wait for all disck activity to stop, then open the app and the system should have reclaimed the memory.  

Windows XP is not as efficient as reclaiming used memory as is Vista, so you could always use a third party memory manager if you are having major resource problems.  The memory manager still has to stop all activity before purging, if not data lose could occur. 

Also, Vue keeps in memory the last operations for you to undo them. If the purge occurred automatically, this option of undoing would be lost. Photoshop has pretty much the same options, and I think it makes sense.
Dunno if you noticed, but with the last update, voluminous data such as displacement & SSS can either be kept in memory or flushed after a render completes. So this option works with purge memory. If this was your final render, you may want to flush the data, or keep it in memory to render again. Same if you don't have enough memory, flushing the data will help you work better on the scene, but it will have to be computed again for next render. I think this can help a lot "older systems" to cope with the high memory and system resources needs of the new functions of Vue6.