They say its easier to change your company to fit SAP than to mold SAP to fit your company.
From what I've been told, this is actually supposed to be a selling point of SAP: They have built tools to fit the processes of the industry leaders, so by buying into SAP, you're buying into the winning way of doing business.
I am not endorsing this opinion or making a claim regarding its veracity, just stating that that is what I have heard.