And there you just showed why we loved our SLRs so much! Nice blurred backgrounds.
I think the photo taken with the 400D is not as sharp due to not enough Depth of Field. Remember with your compact the DoF is something like 6 times more (hence the detail in the background even with the same f/5.6). To get enough detail in this photo, I think you should’ve gone to about f/8 to get enough of the flower nice and sharp.