Does anyone else find those to be very odd limiting values? 1/72" is a standard unit in typesetting, but 3240 looks quite arbitrary, 14400 is 200 * 72 or a slightly more "computerish" 900 * 16, and 75000 is definitely more arbitrary than the nearest "round" limit of 65535.

As a relevant contrast, Knuth's TeX internally uses units of "scaled points" for dimensions, or 1/65536 of a point, and its point is defined as 1/72.27 inch so its precision is approximately 5.36um, and the maximum dimension of a page is 1073741823 scaled points, or approximately 5.758m.