That makes more sense than anything that I have heard.
BTW, I have never heard of a cement suspended ceiling.
The Washington DC subway stations sport concrete ceilings (continuous with the walls). Link to photo is here (scroll down a bit) http://fotot.jarvenpaa.net/en/0000000022 I believe the white rectangular objects visible in each square of the ceiling portions is a light weight screen of some kind, which covers vents and other mechanical items. But the main structure of the ceilings is concrete. Probably a good deal safer than the Boston tunnel design though, due to the self-support provided by the continuous arch, plus I think the grid pattern is due to an underlying structural framework of serious steel (like I-beams, not re-bar). I've never heard of a chunk coming down, and things in DC aren't exactly built by conscientious non-union workers. I think the union-mob infestation is nearly as bad there as in Boston. In the huge blizzard in the late '90s that shut down Congress for a few days, the Congressional investigation into why the roads weren't cleared discovered that at least 2/3rds of the trash collection/plowing trucks owned by the city had long since vanished, presumably sold to the mob by the union guys who were supposed to be driving them every day (and who had no doubt been continuing to collect paychecks for "driving" the long-departed trucks), since nobody but the mob buys stolen trash trucks.