While they look somewhat alike from the outside the actual mechanism that operate within the firearm are in fact very different. The AK-47 series uses a rotating bolt while the STG-44 uses a early form of delayed blow back that later was used in the Cetme of Spain & the G-3 rifle. Form follows function, also the AK-47 series of weapon is a handy carbine good from bad breath range to around 250 yards. 8^)
With all due respect, N, you may be confusing the Stg44 with the Stg45. The Stg45 was the delayed blowback rifle. The Stg44 was gas operated.