You may be on to something, and you're right there is Robusta available that is supposed to be good. Another difference is that American crafty houses are roas

You may be on to something, and you're right there is Robusta available that is supposed to be good. Another difference is that American crafty houses are roasting lighter than in Italy. For whatever reason, Americans are following a different craft and not optimizing their espresso recipes nearly as well as the Italians and not using the same goals and procedures as they do. And frankly I'm convinced some of the roasters simply don't know what they're doing. They've been told that roasting light is good, and they don't realize that light roasting with espresso brewing is risky. Especially with bean types that are known to be acidic.