Just as you wouldn't necessarily believe everything you read in every bike forums post, you shouldn't believe everything you read on every seat post. I had a 26.8 mm SR Laprade post on my Claud Butler, and when I went to replace it with a 26.8 Zeus post, the Zeus post wouldn't fit. Not even a little bit. So I put the Zeus post on my Lambert instead.
Agreed, I've found a lot of seatposts, even Campys that were a) not round, b) had tapered or inconsistent diameters, and/or 3) undersized or oversized.
verktyg
Chas.