De facto, given that the 400'AGL is a certification requirement (as opposed to an operating requirement) from US FAA, I guess it would depend on whether a given country has their own certification standard or not. You certainly raise an interesting point; maybe somebody else can answer it for us.
I am not familar with the performance characteristics of in production Boeings and AB so what I am about to say may be dated.
Accelerating/cleaning up at 800'AGL vs 400'AGL (in your example) may not be "safer." Older jets (707, Gulfstream 2) needed to clean up at 400'AGL in order to increase their rate of climb. In other words, all other variables constant, cleaning up the older jets at 800'AGL resulted in less altitude gained than if they were cleaned up at 400'. Perhaps this is not a factor anymore; I know its not with the Gulfstream, hence the OEI profile goes to 1500'AGL on the newer models.
I think John T is spot-on with his remarks. Airline operators can taylor their profiles to fit their route structure.
Best,
GC