I have to agree for the most part.
I also get notin's argument that the pitching the 8th inning can sometimes be harder, if the heart of the order is up.
But there's something about having a guy like Kimbrel or Papelbon or Rivera pitching the 9th every time you have the lead. It's a sort of comfortable feeling. They will occasionally blow games but they usually bounce right back. It's something you can count on.
As for the pressure of pitching the 9th, I do think it's different. To me it's like a field goal kicker who has a chance to win or lose the game on the last play from say 35 or 40 yards. It's a high-percentage play for them. But the thing is, the whole game is on them, and everyone is watching them, maybe many millions of people. Are you Adam Vinatieri, or Scott Norwood? Keith Foulke, or Calvin Schiraldi? Your career is going to be defined by this moment, and possibly ruined by this moment.