Brits also use the comma between groups of three in communications aimed at native English speakers. The subject exercising the General Conference in 2003 was whether to use a decimal point to mark off decimals or the decimal comma as used by the French (and others) and the resolution adopted simply reaffirms what the 1948 (9th) convocation had resolved:
Symbol for the decimal marker
The 22nd General Conference,
• a principal purpose of the International System of Units (SI) is to enable values of quantities to be expressed in a manner that can be readily understood throughout the world,
• the value of a quantity is normally expressed as a number times a unit,
• often the number in the expression of the value of a quantity contains multiple digits with an integral part and a decimal part,
• in Resolution 7 of the 9th General Conference, 1948, it is stated that “In numbers, the comma (French practice) or the dot (British practice) is used only to separate the integral part of numbers from the decimal part”,
• following a decision of the International Committee made at its 86th meeting (1997), the
International Bureau of Weights and Measures now uses the dot (point on the line) as the decimal marker in all the English language versions of its publications, including the English text of the SI Brochure (the definitive international reference on the SI), with the comma (on the line) remaining the decimal marker in all of its French language publications,
• however, some international bodies use the comma on the line as the decimal marker in their English language documents,
• furthermore, some international bodies, including some international standards organizations,
specify the decimal marker to be the comma on the line in all languages,
• the prescription of the comma on the line as the decimal marker is in many languages in conflict with the customary usage of the point on the line as the decimal marker in those languages,
• in some languages that are native to more than one country, either the point on the line or the comma on the line is used as the decimal marker depending on the country, while in some countries with more than one native language, either the point on the line or comma on the line is used depending on the language, declares that the symbol for the decimal marker shall be either the point on the line or the comma on the line, reaffirms that “Numbers may be divided in groups of three in order to facilitate reading; neither dots nor commas are ever inserted in the spaces between groups”, as stated in Resolution 7 of the 9th CGPM, 1948.
It’s clear that the 1948 resolution was to avoid the anglophone use of commas as separators in large numbers confusing/irritating francophones.
I would agree that for international communications (such as ours) using English as the medium of communication, spaces would be the best choice of separators (and point as decimal separator). Not sure how to make “thin” spaces, otoh.