There are 2 types at dts.com, discrete and matrixed. All Dolby's are matrixed. I haven't noticed any discrepancies in their lists. Are you sure you looked at the right versions of these discs? If you are simply looking at the back of boxes, the Dolby ones will say "5.1", which is accurate, but they will also say Digital-EX if there is matrixed 6th channel encoding.

I find that plenty of 5.1 movies also sound decent converted to 6.1 by my receiver, just like stereo sources can sound good converted with Pro Logic or similar.

FYI, it is DTS-ES and Dolby Digital-EX.