especially if you consider there are devices listed with 0%.

my guess is they do the same as i did when i checked for mobile devices on my site:
look at the OS in the server stats, determine what is counted as a mobile device (fixed list) and then count that in your server stats.

if they did not at one point decide that "Linux armv6l" (and armv5l) is a mobile device, the tablets will never show up. and I guess this is what happened.

on the other hand:
isnt it very flattering for NITs to be considered full-blown computers rather than encumbered mobile devices?