Quote: The diameter of the aperture isn't directly related to its physical size, but rather the apparent size as viewed through the front of the lens.
Sorry, that's not true. The aperture, as reported in f-numbers, is a ratio of the physical aperture and the focal length.
Quote: On a DSLR, it shows F2.8 through the range but I assume that at 210mm, you'll get the same exposure whether it's set to F2.8 or F4
Sorry, that's not true either. F4 is f4 whatever the focal length, because it's a ratio of aperture and focal length.
The Olympus system has a shorter distance between the lens and sensor, meaning it's easier to make larger apertures.
Most people, when discussing lenses, make the implicit assumptions that they can change a parameter and that everything else remains the same. Sadly that's not true, everything is closely interrelated. So using a wider aperture might change aberrations performances, sharpness across the whole image plane, vigneting, etc. There is also a huge difference between a lens that focuses externally, for instance, by moving the whole lens (think M lenses) and a lens that focuses internally, by changing the relative position of the lens elements. The latter will have much more varying performances as you focus or zoom.
Lens design is an art AND a science. It's really not as easy as it sounds. Which is sad