Can someone explain the differences between Post Processing software?

I shoot mainly jpeg. Lots and lots of photos, not much time to post process. I shoot with the 7D. I find that at least according to my standards, when I look at my photos in the computer they do not need much. I shoot mainly sports and landscapes. So cropping is pretty much all I do, with an occasional slight lift of a shadow or slight touch up of contrast or color.

But for the most part I am pretty happy with things as they are out of the camera. So, I have just been using iPhoto on my Mac.

I have DPP from canon. What I would like to know is if there is any difference between iPhoto and other software when it comes to minor adjustments and cropping. I know there is loss to jpegs when you save and the compression. I understand all of that, but so far images that I have adjusted in iPhoto and made comparison adjustments in DPP really don't show much difference.

Can anyone shed any light on this. Is there a difference between the way DPP makes adjustments vs. iPhoto. Will DPP be less destructive to jpegs than iPhoto?

Thanks