Here's a much more powerful example:
Almost totally unreadable:
PDF
Merely somewhat illegible:
PNG
Obviously there's still a long way to go and the 800x600 resolution does make it inherently difficult to display a full A4 page.
But the point here is that Sony's pdf viewer can be improved TREMENDOUSLY. It can't even render a half-A4 page legibly, and that's inexcusable.