Correct. Granted that the threat of bomber attack was far greater than the threat of falling debris, concerns over shrapnel and spent rounds didn't stymie the spread of antiaircraft defenses. What they did do was encourage the spread of helmets and discourage people from coming onto the streets.

Here's a piece from the Journal of Material Culture that talks about children's shrapnel collections in Britain and injuries obtained while collecting shrapnel.

The Honolulu Advertiser has a nice oral history collection about Pearl Harbor that talks about civilian casualties caused by falling rounds.

Funny, I was wondering something very similar a few weeks ago. Here is the response I got: https://www.reddit.com/r/AskHistorians/comments/3egffb/are_there_any_statistics_regarding_ww2_flak_as_a/