Springfield XD missing back piece??

[Barbarossa]

Both of mine are just like that.

[Briancnelson]

The purpose of the cutout is so that the slide will come off properly, and it makes it so you can drop the sear manually with a pin punch in the event you have a trigger malfunction, so you can still strip the gun.

[USMC VET]

Normal

[pkc168]

This is normal.

[Old4eyes]

The small missing plastic piece is an effort to drop weight. Every Micro Ounce counts.

It's a gap to clear the ejector. And funny enough, that gap is on all of the XDs I own.
Don't worry about the gap.
Worry about the fact that Glock owners will ridicule you for touching an XD.

[Bigtwin]

Nothing is missing!

[Just Dave]

Looks like mine!

[quig]

The purpose of the cutout is so that the slide will come off properly, and it makes it so you can drop the sear manually with a pin punch in the event you have a trigger malfunction, so you can still strip the gun.

Correct.