If the point of the HOV lanes is only to reduce congestion, why do they allow 'green' vehicles?
If a hybrid SUV is allowed with one occupant, then so should a bike.
I think a big part of the reason we want to reduce congestion is because congestion causes pollution.
I also agree completely that most of the HOV lanes lead to the urban core where bikes DO take up less space, so even if in the HOV lane itself you have no benefit from a bike, you are still encouraging a reduction in congestion over the total commute.