Pixel editor vs a workflow editor? I don't understand the distinction. I currently use iPhoto that came with my iMac - each slider change the entire photo. I did see another recommendation for Aperture but it was equated to LR4.
iPhoto is a workflow application. Here's the difference:
Pixel editors (like Photoshop) make actual changes to the pixels in the photo. When you save your work, the original photo is irrevocably changed. (Unless you always Save As or create a working copy.)
Parametric editors (like iPhoto, Lightroom, Aperture) don't touch the original raw (or jpeg) file; instead, they keep track of the changes you made in the sliders, then apply all those changes when you export the photo. This means the original file is untouched, so you can go back and start over, or do something different if you want.
When you move slider in iPhoto, you are changing your view of the photo, but you are NOT changing anything about the actual original file. You're just making edits that will be applied later.
One cool feature of iPhoto, LR, and Aperture is their ability to manage your photo archive for you, keeping track of all your images and allowing you to organize and search for photos in many different ways.
I rarely open photos in Photoshop any more, unless I need to do heavy retouching -- which is possible in Lightroom, but a lot easier in Photoshop.