Dudley
The XD was originally chambered in 9mm, and the frame was beefy enough to stand up to 40 S&W (Eastern European ammo is loaded a lot hotter than US SAMMI spec). The pistol was originally named something different and only had moderate sucess in the US, but Springfield bought the Croation company making the pistol (so I have been told) and renamed the pistol. The reason for the delay in a 45 pistol is probably the cartridge is a lot bigger than the 9mm/40S&W, so some parts will need to be scaled up and retested.
Str8_Shot