Microsoft, as well as many PC vendors, have faced lashback from the "Vista" labeling system, which many have claimed is ambiguous and doesn't do enough to differentiate between what a Vista capable system and what a Vista Premium capable system is. Some have gone so far as to sue over it. That said, Microsoft will be updating the requirements a machine will need to be "Vista Premium" labeled. In about a year from now, any machine sold touting the Vista Premium label will need to include a DX10 compatible GPU, which directly corresponds to Microsoft and other developers getting ready to release many DX10 titles over the next year.
Will this create more confusion? It seems that for a while, you might have a large number of machines labeled "Vista Premium" capable, some of which have DX9 cards and some which don't. However, with the two major vendors already supporting DX10, it is unlikely that any machine shipped with Vista Premium would appear without a DX10 card in the first place. However, could it also indicate future label changes as they deem fit? In that case, what good would any label serve if it can be invalidated by future iterations?