The versions here, in mm, are the official sizes according to http://en.wikipedia.org/wiki/Paper_sizes at 2005-01-25. (The ISO entries in the below table were produced mechanically from the table on that page.)
(The rule seems to be that A0, B0, ..., D0. sizes are rounded to the nearest number of mm from the "theoretical size" (i.e. 1000 * sqrt(2) or pow(2.0, .25) or the like), whereas going from e.g. A0 to A1 always take the floor of halving -- which by chance coincides exactly with flooring the "theoretical size" for n != 0 instead of the rounding to nearest done for n==0.)
Ghostscript paper sizes are given in gs_statd.ps according to gs(1). gs_statd.ps always uses an integer number of pt: sometimes gs_statd.ps rounds to nearest (e.g. a1), sometimes floors (e.g. a10), sometimes ceils (e.g. a8).
I'm not sure how ghostscript's gs_statd.ps was calculated: it isn't just rounding the "theoretical size" of each page to pt (see a0), nor is it rounding the a0 size times an appropriate power of two (see a1). Possibly it was prepared manually, with a human applying inconsistent rounding rules when converting from mm to pt.