Why does iPhoto 'soften' when you use 'Straighten'?

It's hard to explain this effect in words, so I've done a picture to show it:

As you can see, iPhoto drastically softens (in my opinion) when you rotate ('Straighten') a picture, compared to Photoshop's Rotate command. I've deliberately enlarged an area of writing to demonstrate the effect : there is a very slight softening in Photoshop but it is barely noticeable compared to iPhoto.

Just to reiterate what I said in the other topic, I've always noticed this, in iPhoto '06, iPhoto '08; on a G4, on a G5, and now - especially - on a Core i5 iMac.

I guess there is no solution. I just wanted to know that this is not my imagination, that others have noticed it too?