That is what Microsoft says here and here and has been validated by experts in the SharePoint community like Spencer Harbar:
A server can be installed and run on less, but unintended consequences will follow. E.g. services not provisioned properly (I'm looking at you, UPS), poor performance, general mayhem.
4GB is the bare minimum. From what I have read and have been told, anything less will be taking your life into your own hands.
Does anyone have any validation or invalidation of this particular requirement? Has anyone be able to get certain server roles running on less than 4GB of RAM (WFE, APP, Office, Index)?