So steemit.com is cutting off the graph, but basically:

If n is the number of Steem Power you vote with (simplified), then say you have 100 and someone else has 1000.

N:
100 = 100.
1000 = 1000.

N log N (with log base 10)
100 * log(100) = 100 * 2 = 200
1000 * log(1000) = 1000 * 3 = 3000

N^2 = N* N:
100 * 100 = 10000
1000 * 1000 = 1000000

So a n^2 curve favors the rich, an n curve favors everyone, n log n favors the rich, but not by much.