Ditto when I came into Rome with a Canadian passport, was only asked to show the front cover. The immigration dude did not claim to have second sight, however.
He was obviously a graduate of the special Advanced Insouciance course many immigration guys attand. Putting a stamp on the bottom corner of page 32 of a passport that’s hardly been used is an important skill. Putting a small stamp right in the middle of one of the few blank pages, so it cannot be used for a full-page visa, is another one. 
Kipper - it seems to be standard procedure these days. Unless you like someone they’re interested in, they just wave you though. I wouldn’t say it applies to (say) Nigerian PP holders, though.
My first ever stamp was for the US (British citizen flying from Toronto to Atlanta). For some reason the Lady felt the need to stamp right in the middle of the passport on about page 20.
At least Lithuania (my only other Country so far - I only seem to travel within the EU) got both on the first available page.
Really? I’ve been to thailand several times and have never had a problem. Interesting, I guess it stands to reason though.
It was years ago, but you used to be able to ask customs agents on trains to stamp your passport, even though it wasn’t necessary, as you went through each country.
As far as eagle-eyed passport control:
Back in the Iranian hostage days, the Canadian government gave an American a fake German passport in order to escape Iran. At the airport, an observent Iranian guard noticed the name on the passport was Hans A. Muller and demanded to know what was up, “Germany does not allow initials to be used in names on passports.”
The quick thinking American said quietly, “My parents gave me the middle name of Adolf and I have been embarrassed about it so they made an exception and let me use an initial instead of using my full middle name.”
The Iranian guard bought the story and let the American get on the plane.