Certain older games like Blood 2, Messiah, Tonic Trouble, Frogger 2, ... run in fullscreen mode but have a border around it.

While many games from the same time like Interstate 76, MDK, NFS4, etc don't create any border.

Why do some games get a border while others don't?

(I am aware of the DXPrimaryEmulation and ForceSimpleWindow, I am looking for "why?"?