Not all HDtracks are upsampled. I've gotten 44.1khz/24bit releases and some 48khz/24bit as well. Just depends on the album. Older ones recorded to tape tend to get 96khz, but some modern albums are at 48khz (Hybrid Theory is one I believe). Its nice to get high quality copies without having to resort to vinyl rips.
The new Deftones album is far superior on HDtracks, not nearly as squashed and sounds much deeper.