With right click on every tile I have the option to make it larger or smaller, except the IE 10 tile - it is always small (at least on my PC), and the right click doesn't show such an option.
IE 10 does not have a larger Tile option because it does not require it. Though App developers are free to provide options for both the Tile sizes, the larger Tile is preferred only if the Tile has some Live info or notifications to display. Windows's inbuilt Apps have been designed in a way that Apps such as Music/Videos/Photos/People/... which require more space to display Live-info or notifications have a larger tile. Other tiles such as IE/Camera/Reader/Maps/... can be pinned as smaller Tiles only. IE for instance does not have any notifications to display, neither can it display other Live info as of now.