As explained in the documentation of doc mean, the dimension to operate on can be defined by the second input:
x = rand(10, 10);
m_dim1 = mean(x, 1);
m_dim2 = mean(x, 2);
If mean(X) and mean(X.') reply the same values, either X is a vector or the means are equal. mean(X) without specifying the dimension operates on the first non-singelton dimension. This is risky: You save half a second during typing, but might spend hours with debugging. So prefer to define the dimension explicitly, because sometime Matlab's smart decisions to guess what you want, are too smart.
