In pairs, I understand the technical advantage of pairing a tall man with a much smaller woman, and I find this type of pair aesthetically pleasing, too. I personally prefer a height difference of 8 to 12 inches in a pairs team. Gordeeva/Grinkov had about a 9-inch differential, and I thought they were beautiful together.
In dance, the differential doesn't need to be as large, but I think it looks best when the man is at least 3 to 4 inches taller. Sometimes it's nice to see a team with a taller man, such as Dubreuil/Lauzon or Lang/Tchernyshev, but teams that are more closely matched in height, such as Belbin/Agosto and Navka/Kostomarov, can also look very good. I agree however that Denkova/Staviyski are just too close in height. As much as I try to ignore this when watching them, I just always keep noticing it and being distracted by it.