The distance I use my tablet is not the same I use my laptop, and the first one is always shorter than the second one: tablet is used at most at arms length, while laptop is at least at arms length.
You can't compare DPI as is, because viewing distance has to be taken into account before one can make sense of that value A proper, directly comparable unit would be the size of a pixel in arcseconds (which would carry the device's own typical viewing distance). Here's Phil Plait (of Hubble fame) explaining the stuff [0].
I'm trying to imagine how you go about using a laptop from more than an arm's length away, but all the mental images just make me giggle.
I agree that there is a minor difference in viewing distance between a laptop and a tablet, but I think they're still comparable, in contrast to, say, a TV.
You can't compare DPI as is, because viewing distance has to be taken into account before one can make sense of that value A proper, directly comparable unit would be the size of a pixel in arcseconds (which would carry the device's own typical viewing distance). Here's Phil Plait (of Hubble fame) explaining the stuff [0].
[0] http://blogs.discovermagazine.com/badastronomy/2010/06/10/re...