Here is an article discussing the downgrade of the digital after Feb 2009. NBCU working to ensure that operators display proper aspect ratio with with receivers.
NAB 2008: NBCU Tackles Digital Downconversion - 4/15/2008 5:22:00 PM - Broadcasting & Cable
NAB 2008: NBCU Tackles Digital Downconversion - 4/15/2008 5:22:00 PM - Broadcasting & Cable