Why does ArmA's Bump Mapping Sink Instead of Raise?

[Quake 1]

If you crawl and look at the ground a little bit ahead of you, you can see that the bump mapping is done really oddly. For some reason it sinks the texture forming the bumps from the bits that don't sink, instead of raising the bumps. If you go up to a building and look at where it meets the ground, it has the illusion of it floating due to this style of bump mapping.

This is the first game/sim I've seen do bump mapping like this. The only time you see bump mapping sink in other games, is when the bump map is for cracks or bullet holes. I've never seen bump mapping sink the entire texture minus the bumps.

I was just wondering why it's done this way instead of the normal way?

[Shadow NX 1]

Because it isnt a Bumpmap, Bumpmaps are also there but they dont create the overall look that you mention.

Downside is as you said it sometimes look like things float from some angles.