I was about to post something similar to this. However, here's what I think about it. And someone tell me if I'm wrong.
When we change the sliders it automatically goes becomes a "custom" difficulty. Meaning that there's non such thing as All-Madden with sliders, All-Pro with sliders, etc. There's simply default Rookie, Veteran, All-Pro, and All-Madden. If you change a slider the difficulty is now simply "Custom."
If this is the case, I actually like this a lot better because it suggests there's nothing under the hood with the difficulty settings that adjust the game mechanics, AI, etc.