800 for the average adult beginner hass been well observed for a long time. Arpad Elo even mentions it in his book:
The Evaluation of Chess Players Past and Present.
It is tough to prove of course since beginners rarely play in tournaments and thus tend not to have ratings.
The official USCF and CFC/FCE classes for tournaments are:
Code:
Open
Expert 2000-2199
Class A 1800-1999
Class B 1600-1799
Class C 1400-1599
Class D 1200-1399
Class E 0-1199
There are usually more E players than D.
When Elo developed the system a bell curve centered at 1500 roughly represented the members of the USCF at that point in the early 50's.