I've seriously never heard of this, and am middle aged and married with kids, and lots of married friends.

A few friends had 2-3 tiered cakes, but they were always real cakes, just quite boring internally (plain vanilla sponge). At most, there were posts through the middle to round pieces of cardboard/wood/something in between the layers for support, for one wedding I went to. Most others were just big elaborate "normal" cakes.

I always assumed the crazy big American wedding cakes on TV were at least mostly real, maybe with supports and levels to structure it.