I bought my car in Texas, and there was no license plate bracket on it. Not sure if that's normal or if my dealer sucks. They just screwed the paper plates directly into the bare bumper with a cheesy dealer plate frame. I wanted to slap them for that. With metal plates, the first car wash I went through bent half of the plate up about 90 degrees, so I think it really needs some sort of support.
For now, I took it all off and am going to have the holes in the bumper fixed. If I get hassled about it, I'll add a bracket of some sort.