Gee, I don't know, perhaps the fact that he makes between 30-35 starts every year without fail, and has a career ERA just north of 3. Take off the anti-Cub glasses for a minute and look at the numbers. I am not necessarily saying he tops the list. Far from it, but you are an unabashed homer if you can't recognize that he is certainly more involved in the conversation than Sheets. His ERA the past 3 years have been 3.41, 3.95 and 3.22 and going up this year(very luck based peripherals). There is no way Zambrano should be in the same list of true aces as Webb and Santana if you are going to leave Sheets out of the mix. Over his last 3 seasons his ERA is now 3.56 compared to Sheets 3.49 and that is with Sheets having one of the worst defenses in baseball behind him in that timeframe and Zambrano having one of the better. If you compare peripherals Sheets beats him there as well. If you go back 5 years instead of 3 Sheets still beats him in ERA. The only knock that is valid on Sheets has been health and well that is pitching, they get hurt a lot.