@ Kangal: Firstly, what are you doing editing your post to quote what I wrote after your original post? It makes it hard to follow the the flow of the discussion and see what new stuff has been written. Keep the edits for fixing mistakes and make a new post for adding new comments or clarifying your original points.

Now, to address the rest of your post, it is all based on a flawed assumption about viewing distance. I can tell you that I typically hold my N900 between 10-20 cm from my face; while I may struggle to see individual pixels at 20 cm, I can see them at 10, therefore >220 PPI clearly isn't too much since the N900 has 266 PPI and I can still see individual pixels.

At one point in your post you make the assumption that a 10" tablet would be used at 50cm, I don't have my netbook screen that far away when I'm actually using it (unless I'm watching video), so why on earth would I stretch my arm to hold a tablet at that distance. For a tablet computer, if the resolution is so high I can't see the detail I can bring it closer to my face, there is a point where increased resolution will be superfluous and it does depend on viewing distance, however most devices these days (generally excepting TVs) don't come close.