Not sure, I have a crystal clear Pic on Netflix , Youtube and most streaming video sites. Since the 2 things you mentioned are streaming video my first suspect is Intenet connection, so Ii recomend downloading the timescapes trailer TimeScapes Download Trailer and then taking some video with the device yourself If both the downloaded video and video you take look fine then that indicates it is either the internet or the apps themselves. Since others do not have that problem with the apps.....
My screen is crystal clear as well, as it was already said I would just do as previously mentioned and try out the Timescapes trailer and another video and compare.
That is why the times cape video is a good control. It is a very clear video if it appears grainy it may indicate the screen. Any other video leaves open the possibility it is the video's fault. How it was recorded, downloaded, encoded etc.