Alot of displays have this, and i know it as 'banding'. You should be able to find this term on google. My monitor i plug into my mac has this sometimes when there are strong gradients of colour (one colour fading into another). Im not sure if my mac screen is like it though.

How bad it is depends on the screens colour depth and various other factors. The X10 must have a better display.

Hope i make sense! Im very tired and typing on my N900 so no spell checks! :P