Why Are The Numbers Hidden (or am I just lazy)?

I have used an ATC for over 10 years. On the front of packages and advertisements I am used to seeing the range of 'handled' rope diameters as 7 to 11 mm. But I learned from experience that rapping on smaller than a 9.5 single seemed a little too fast for my weight.

So the recent GriGri discussions got me reading device instructions for it and the ATC. For the regular ATC & ATC Guide, a picture shows ranges from 11 down to

a) 9 for single ropes (I like double biners for the lower half mm)
b) 8 for double ropes (much bigger than 9 seems too fat)
c) 7 for twins (never tried twins)

Call me lazy for not seeing the breakdown sooner!!

And for the GriGri 2, the up front stuff indicates a range of 8.9 to 11 mm. And sometimes nearby (sometimes not), the 'optimized' range is given: 9.4 to 10.3 mm. Has the smaller optimized range surprised anyone in practice? I haven't really used a GriGri 1 or 2 but know their intended ranges are not the same.

The numbers are vague (if that´s the right word) because there is no standardised test for belay device performance and no definition of what adequate performance is. For whatever combination of climber/rope/type of use some climbers find the performance adequate and some don´t.
Some manufacturers confuse the issue by writing different things in their advertising compared to the instructions:-)

It would be nice is someone who has ever worked for BD or Petzl would pop along and give us a hint of how they come up with the numbers.

Thank you, Jim. Not many of us can say we've designed a belay device for a major supplier of climb equipment.