The other thing about Lego is that it's a bit trickier to clone than you'd think. Most of the other 'compatible with other major systems' brands don't come apart as well as Lego does.
It seems part of the trick of Lego is to make things that are appropriately easy to take apart, as well as put together.
I guess that "plus-like protrusion" is designed to fit "tubes" on the high bricks, primary use being removing low bricks from high bricks. I guess one could use two separators side-by-side to firmly hold 4x2 brick, IIRC 2x2 had one "tube" and 4x2 had two "tubes".