I know you asked about the differences, but if I may make a recommendation:-
If you are after a really good quality Macro lens, and have a good budget, consider the Carl-Zeiss Makro Planar T* 2/100. If you have a Nikon, you want the ZF.2 version (Nikon mount). I own the Canon-mount ZE version. At 100mm, and with an f/2 aperture, it takes some truly STUNNING photographs.
See here and here for examples.
Of course, you have to work for it. The lens does not auto-focus, so it's all manual, but the throw on the focus ring is so silky smooth it is a joy to use. You can also take advantage of the AF confirmation light in the viewfinder to know when it's focussed.
It's built like a brick, with a solid metal body, making it a weighty lens, but comfortingly so.
At f/2 the depth-of-field, even on my crop-sensor EOS 7D is razor thin, and as a friend of mine is fond of saying "Breath, and it goes out of focus", and you will end up with a lot of out-of-focus pics where the plane of focus is just out from where you wanted it to be. So to take good pics close up does take practice, and it can get very frustrating. But practice, practice, practice. And if you are able to use a tripod then that issue goes away.
It can be used as a nice portrait lens too, with it's shallow depth-of-field being able to isolate your subjects well, with high contrast. An example is here.
It's also a very expensive lens - I paid just over £1500. (Ouch, but I had wanted it for over a year, and saved specially for it).
Really, the negatives of this lens (heavy, no AF, expensive), all seem to become utterly insignificant when you see the results of what it is capable of. Bokeh is dreamy, whilst subjects are pin sharp.
Here is a link to the official Carl Zeiss site for that lens.
My complete set of pics taken with it on Flickr is here.
I'd say this is what defines the step up to professional quality in the macro lens range. I can't recommend it enough. Worth saving for...