Selling Your Vote

I recently read a comment by "Marcus" on the EconLog:
Why is it OK for politicians to sell their votes (like we saw with Republicans and the bailout) but it's not OK for the rest of us?
This is a really excellent point. It is against the law for me to trade my vote for economic benefit or to trade my vote with someone from a different state. But through the power of horsetrading and pork barrel politics, congressmen trade their votes every day. They say I'll vote for "Bailout X" if you stick in some cash for a new bridge, or I'll vote for "Bailout X" if you vote for "Spending Bill Y." Aren't their votes more important than ours? Shouldn't they be held to a higher standard, since every one of their votes represents millions of us? What's good for the goose . . .