This exact same thing happened to me. I think the other shoe has dropped at Netflix. They're tired of maintaining mutiple servers for multiple codecs. I was gifted an xbox360, checked-out their netflix plugin, then installed Win7, the legacy player and the vmcNetflix plugin on my HTPC. It insists on the silverlight player, which led me to believe that the Xbox application may have opted me in. This turns out to not be the case. I've been a member of netflix for 4+ years and was an early adopter of their streaming efforts as well.
HTPC: Intel E6750, 4 GB DDR2, nVidia 8600 GT OC, 2.8 TB Storage, 2 Hauppage 2250s, LG GGC-H20L, nMEDIAPC Black 288BA, Win7 Ultimate 32-bit, 3.7 TB WHS, Xbox360, DMA2200, DMA2100, 3 1080p displays and an old-school CRT.