Andreas- the British Army had a Brigadier (non-General) rank in World War I; between the wars they had a Brigadier General rank that replaced it but by the time of World War II it reverted to a non-General Brigadier rank. Why I don't know. Again perhaps one of our British friends knows the rationale behind it.
Sorry, but this is incorrect. The British used the rank of Brigadier-General during the WWI, and it was replaced by Brigadier in early 1920's, I think.
The reason for this change was reportedly to make the Royal Navy Commodores fully equal to the Brigadier-Generals. While Army Brigadier-General was a general and had the perks of a general, Navy Commodore wasn't an admiral and didn't have admiral's perks. Thus Commodores and Brigadier-Generals were made equal by 'demoting' the Brigadier-Generals to Brigadiers.
Rotmistrov was a Chief Marshal of Tank Forces, an inferior rank to Marshal of the Soviet Union. It ranked with General of the Army. The great authority is website marshals.narod.ru
Sorry, but again this is incorrect. The very web-site you quote indicates that Chief Marshal was a rank equal to Marshal of the SU. An 'ordinary' Marshal was equal to Army General. (Yes, pretty weird system, and Army Generals weren't happy with it, but still that was the way it was!)