Well for starts most meads also include the addition of yeast nutrients since honey can be a bit low in nitrogen if I am not mistaken, but more to the point, there is more to honey than just sugar.
If you smell honey there are quite a lot of aromatics going on, and if you taste it, there is more than just plain clean sweetness like in table sugar. Essentially, the assumption that honey is just the same as table sugar in the alcohol equation is wrong as I believe you implied and wanted to know more about.
Now, making mead can be quite tricky, especially dry meades because great care and patience is required in order to preserve all the delicate flavors and aromatics without the aid of many residual sugars.
With sweet meades, they can be quite a bit more forgiving, but tend to get kinda boring after the first glass.