One reason you need to specify something beyond "Hallertau" is because of "Hallertau Blanc". This has AA of 9-12% and is described as mostly an aroma hop for American beer styles such as IPA "with moderate to strong notes of pineapple, white grape, fresh lemongrass stalk, and passionfruit characteristics". I once grabbed a package of that at my LHBS and the cashier asked me if I knew that this was nothing like the other Hallertau hops. In fact I wanted Hallertau Mittelfruh, but they were out of that so I grabbed this one instead. He saved me by alerting me to the difference.