Hi, icons can be made up of several pictures (of different sizes) all together in 1 file. For example, most icons contain a minimum of a 16x16 picture and a 32x32 or 48x48 picture.
Icons are basically embedded into a program when it's created. So if the icon that is used for a program only has a 32x32 icon, that's all you will see.
Example: The first icon has multiple pictures included (see them on the right). The 2nd icon has 2 pictures, the last icon has 1 picture. See how they look in Explorer below that.
You can always create a shortcut to a program and use a custom icon for the shortcut. You just need to find a good high resolution icon with multiple images in it.