Please note that I cited the 420s, not 420. It's under 4 pounds, which is half a pound lighter than the new mpb. It's slimmer than my 15" old-gen mpb, although I believe the retina is slightly thinner still.
Every MBP since the unibody design is 0.95" thick(of course except for the new retina one) and the T420S is 21.2mm-26.0mm thick, how is it slimmer?