Nice point, Wogpotter, I'd forgotten that it was originally designed for use in the Martini-Henry.
The considerations to ease of extraction are no doubt based on the known propensity of the .577-.450 M-H to suffer extraction issues during prolonged rapid fire.
It's theorized that rifle problems contributed to the British defeat at Isandlwana. Being caught in the open and faced with a large number of Zulus required the British to lay out as much fire as they could, as quickly as they could.
Once the cases started to stick in the chambers, the extractors either tore the heads off the composite cartridge, the neck ripped off in the chamber, or the extractor lost grip on the rim, leaving the rifle badly jammed.
Interestingly, the US suffered the same kinds of issues with early Trapdoor rifles chambered in .50-70. The extractor was very small on the Model 1866 Trapdoor and, combined with the soft copper folded-head cases, proved to be a big problem.
Got to agree, though, that bashing the .303 Brit on those points is kind of silly, and is like bashing the telegraph because we live in a computer world.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.