photographers please answer ..?

Perfectly normal. What you have is called a variable aperture lens. It's the cheap kind of zoom lens. There are constant aperture zoom lenses that don't change aperture size as you zoom. They are usually faster and significantly more expensive.

Because over 200mm or so, manufacturers have not found a viable way of maintaining a wide fixed aperture in zoom lenses. They could, I suppose make it f/5.6 across the range but feel they may as well give you an extra stop where they can.

It's a variable aperture zoom, which means at its shortest length, the aperture is at its widest at 4.5. At the longest focal length, it will get smaller, dropping down to 5.6, but don't be mistaken, if it's an L lens, it (probably) has excellent glass!