Here’s Microsoft’s official statement:
"We have used Metro style as a code name during the product development cycle across many of our product lines. As we get closer to launch and transition from industry dialog to a broad consumer dialog we will use our commercial names."
Rumor has it to the reason of sudden description changed is the possibility of legal threats by German retail company, Metro AG. Due to this sudden description change, Microsoft has not had the time to announce a new name. For now it's simply "Windows 8-sytle UI".
