Tony,
Yes I noticed that, whereas the 600psi has triple vacs, possibly a space issue, with the bigger pump. Possibly the thinking is that for hard floors the pressure is more important than the vac, so long as the vacs is sufficient. I must admit that when I use the 'T' Wave on hard floors, I have the psi up tp 1200 for ceramics, but the vac on its lowest setting with the vac relief on the SX12 fully open, and often wish I could reduce the vac more, to prevent lock on's.
Dave