They probably have a hardware decoder, similar to my (dated) DXR2. I think the DXR3 had pretty sweet support for Linux and it is just a Zoran chip anyway, which the Linux Media Labs cards have as well (although I am not a guru of this stuff, so don't flame too hard).
um, DXR3 is a Sigma EM8300 chip exactly like their Hollywood+ card. the LML33 card is a MJPEG capture card similar to the Pinnacle DC10plus which is based on a Zoran chip. You're comparing apples, oranges, and fenceposts here.