Some stats count unique visitor totals of each Browser. Other stats count page hit totals of each Browser. Then you have ones that mess around with not includ

Some stats count unique visitor totals of each Browser. Other stats count page hit totals of each Browser. Then you have ones that mess around with not including all of the particular Browser's versions. And there is no telling who's getting a world-wide sample, who's taking out some coutries, who's samples over-represent a country because their traffic collection base is there, etc.