I suspect most high ranking government officials in the US could make significantly more in the private sector so it's hard to claim there's a high scale of pay for politicians -- at least in the US.
So basically no one expects to make money from their paycheck, but rather go into politics for the fame, connections, and other intangibles.
Position, connections, and influence go a long way before you even commit a crime.
Look at Harry Reid as an easy example.
They can trade stock knowing certain laws will be passed or bills introduced that will have an effect.