Where do people get this mis-information?
BD supports the following codecs: MPEG-2, H.264, and VC-1.
HD-DVD supports the following codecs: MPEG-2, H.264, and VC-1.
The initial version of Sony's authoring software apparently only supported MPEG-2, so early BD disks were encoded as such. Some currently shipping disks may still use MPEG-2 (probaby because some people didn't want to upgrade their authoring software).
In any case, it's up to the developers/publishers which compression scheme they use. It has NOTHING to do with the capabilities of BD or HD-DVD.
"The initial version of Sony's Blu-ray Disc-authoring software shipped with support for only 1 video-codec: MPEG-2[citation needed]. Consequently, all launch titles were encoded in MPEG-2 video[citation needed]. A subsequent update allowed the content producers to author titles in any of the 3 supported codecs: MPEG-2, VC-1, or H.264[citation needed]. The choice of codecs affects the producer's licensing/royalty costs, as well as the title's maximum runtime "
So yes blu-ray supports the same codecs but the studios have to pay more for them.
I would say the majority of BD titles thus far have been done with mpeg-2 compression.