That's close to what I've measured:
Plastic (SKS, Zefal, PB, with steel stays) in 26 X 45-55 sizes are about 1.5 lb.
Honjos, 559 X 50 or so: 1 lb.
I didn't get around to measuring my 700C PB 35s or my 700C VO aluminum 35-40s, and if I measured my 559 X 50 Berthouds, I forgot the number.
But I swear that the PB Cascadias, 65 mm, 700C, that I recently took off my Matthews weighed an even lb, with the cute little but beefy rubber flaps front and rear and steel stays -- but, shortened, to attach about 1/3 of the way down from the crown -- in front; and in the rear, missing altogether, as the rear rack has a boss to provide a 3d direct mount; also, the fender was about 2/3 length -- just long enough, with flap, to keep goop off the rear lamp.