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This is possible because Seeing (i.e. detecting) something and resolving it are two different things.
Suppose your resolution limit is 3 units of angular size. Now suppose you are looking at an object that is 9 units wide but has a dark gap through the middle which 1 unit wide. Somebody now tells you that you can't possibly see the gap, being a third of what you can resolve. You then prove them wrong by seeing it anyway. That's possible because the integrated brightness of the middle 3 units is lower than that of the 3 units on either side. By resolving that difference in brightness you have detected the gap. But that doesn't mean you've resolved it.
On Saturn's rings, this effect becomes apparent when comparing the view of the Cassini division through different apertures. Smaller aperture: wider and lighter, larger aperture: thinner and darker (relatively speaking).
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