I was just thinking about when I was an omni, and probably the average omni diet.
RDA in UK for calcium is 800mg, 1000 in the US.
cereal with milk - 200mg, cheese sandwich.. maybe 250... yoghurt after dinner..less than 250 probably. That's less that 700mg. Yes, they may be getting extra from other stuff. But how many Omnis have that much dairy every day? Not all of them. Plenty could have toast for brek, something else for lunch..etc and basically get no calcium.
Since going vegan I think one thing that is englightening is that I pay more attention to nutrtional needs rather than really not thinking about them much when i was an omni.