For blitting, you are using absolute coordinates and so a change in device resolution causes a change in change in blitting positions relative to the screen. If you don't want that, define yourself a reference coordinate system and scale everything based on that. For example, "blit" as if your screen would be 800*480 and rescale the values accordingly before doing the actual blit operation to match your device's resolution. Keep in mind that different aspect ratios exist as well.
For 3D models, it shows the same as long as the aspect ratio remains the same. If not, it will adjust vertically by default. In other words: The horizontal field of view will always be the same, the vertical will be adjusted to prevent the rendering from distorting.
You can modify this behaviour, but this is how it's by default and that should actually be what one wants in most cases.