The only two airlines (on which I regularly travel) that do this are BA and BD. I assumed it was a UK airline thing. KL, OS/NG/VO, LO, LH, AF, MA, OK have never asked this of me.
Also, I was quite surprised at which part of the BP you retain in the US and Canada. Standard, over here, is that they retain the larger part of the BP (with the ticket insert - if ATB, it can be inserted, stapled or printed over, depending on the airline) and you retain the stub only. This has a slit or a hole for hangers. As it's credit card sized, it's quite convenient to keep hold of...