It's more than a "bully pulpit" thing, as the Presidenat and Congress do indeed have an impact on federal laws as they apply to gays, especially if married. For example consider income taxes - if Congress wanted they could extend joint filing opportunities to gays who have been legally married in those states that allow it - right now a legally married gay couple can not file as "married" on their taxes, due in part to the "Defense of Marriage" act passed under Clinton (now if you want to talk about a flip-flopper on this issue Bill Clinton is at the top of the list). And the federal government could mandate things like insurance coverage for domestic partners. So it does matter what the President and members of Congress think on the issue.