  A result of Jost and Zuo is used to show that for a large class of
finite-dimensional hyperk\"ahler quotients, the only L2 harmonic forms lie in
the middle dimension, and are of type (k,k) with respect to all complex
structures. The argument is extended to some moduli spaces which appear as
infinite-dimensional quotients such as Higgs bundle and SU(2) monopole moduli
spaces. In the latter case we recover some of the S-duality predictions of Sen.
