I imported a 432X163 png image to the project, than dragged it into “splash image” at player settings. when I buld&run the game, the banner isn’t appearing… why? =]
I checked your image and yes. It does get stretched. I got basic Unity (not PRO) and I have the same problem. I solve by:
One. finding original file in NameOfYourGame_Data folder.
Two. In that folder is ScreenSelector.bmp file. I don’t know how but it gets stretched to 512x128 (powers of two even if I have it unchecked).
Three. Simply open your file splashscreenbanner.png (even MS Paint will do as it doesn’t need transparency) and save it as ScreenSelector.bmp in NameOfYourGame_Data folder and replace file that is already there.
Four. Enjoy! 
I just ran into this myself. @tomer2911 is correct - you need to change the texture mode on the image you want to use as the banner. Click the image in your Project panel and in the Inspector, change Texture Type to Advanced. Then change Non Power of 2 to None. Apply the change. Fixed!