"Yeast nutrient" usually is, or contains, DAP (diammonium phosphate). DAP provides YAN (yeast-available nitrogen). In wort fermentations, your YAN will probably always exceed the yeast's requirements. It's all the "other" stuff your yeast needs that's the problem. High-yield commercial farming may result in malt that is deficient in minerals and nutrients that your yeast need.
Servo is specially grown yeast that have high amounts of minerals that yeast like. From the manufacturing descriptions, GoFerm from Lallemand sounds like the same thing. I haven't used Servo, just because of the price tag, but I do intend to track down some GoFerm and try it. Fermaid O also sounds similar. I'm not really sure what the difference is between that and GoFerm.