I counted the number of DualDisc releases as listed on the Quadrophonic Quad web site, by record label. There are 88 releases with Hi-Rez DVD-A mixes, but 70 of them are from Silverline, whose mixes are generally considered the worst in the business (junk). There are 39 releases with Lo-Rez Dolby Digital 5.1 mixes (including the Foo Fighter's disc). I don't know how all of these record labels are releated to Sony, but it sure seems like there are a lot more companies besides Sony putting out Low-Rez 5.1 mixes on DualDiscs, or worse yet, no surround mix at all.
DualDiscs with Hi-Rez DVD-A 5.1 sides:
Decca 1
Dreamworks Nashville 1
Fan Club Ed 1
Interscope 5
Limited Ed 1
Silverline 70
Universal 5
Verve 2
Warner Bros 1
Rhino 1
Grand Total 88
DualDiscs with Lo-Rez DD 5.1 sides:
Columbia 30
Decca 1
Jive 1
RCA 1
RCA/BMG 1
Silverline 3
SRG Records 1
Universal 1
Grand Total 39