I found Clarence E. Simpson right away, but do not identify Robert yet.
Go to entry 778 in the WW II GenForum you posted this message in.
This will bring up a message posted by Mr. Russlie 2-23-2000, who gives the direct posting for overseas burials and missing but memorialized dead.
Click on that and follow the instructions thru American Dead, WW II, and enter SIMPSON where directed.
This brings up a list including 128 dead or missing military personnel named SIMPSON.
Clarence appears right away. There were probably 12 Roberts, but none fit your criteria.
In case you don't get thru, here is the data I found:
Clarence E. Simpson Corporal, U.S.Army S/N 39094809 United States Army Entered the Service from : CA Died : March 6, 1944 Missing in Action or Buried at Sea. Tablets of the Misssing at North Africa American Cemetery Carthage, Tunisia Awards: Purple Heart
The printout features a beautiful cemetery setting, with the flag at full mast and long rows of white crosses. Again, if you can't call this up, I will be pleased to mail my copy to you, without charge, of course.
I hope this helps, and that you locate Robert soon. (I am going to continue lookin for him too.)