You even get this on the iPad for example. But throw a 2D object moving quickly sideways, especially if your graphics are high contrast, and you get blur-ville. more towards the outside edges of the screen you notice it. With 3d it doesn't get noticed so much because even though you move into the screen, relatively speaking the stuff nearer the middle of the screen doesn't spatially move sideways at a very fast rate. 2D scrolling is the worst case, unfortunately. Nobody thought about the effects of fast moving objects creating a blur, and especially nobody thought about 2D games where objects typically move sideways and often at a fast speed. The response times suck on almost all of them. This is something that basically happened when we all shifted from Cathode Ray Tubes and multisync monitors, to the TFT/LCD flat panels.
You could get several of the previous video frames basically interfering with the current frame and causing detailed sprites to turn into blurry streaks. It might not matter much for like watching a movie or something but for getting crisp, sharp, fast-moving 2d objects, it can be a nightmare. In other words, there is temporary ghosting from previous frames which creates a kind of motion-blur effect. The rate at which the pixels in the monitor can transition all the way from white to black is much slower than a 60hz refresh rate. I bet you are on an LCD-type flat-panel display. It's not what you're doing in your game, it's your monitor.
