Recommended heart rate ranges are based on broad statistical averages of the population. And like most averages, it is a pretty good predictor for about 1/3 of the population, somewhat useful for another 1/3, and less useful for the remaining 1/3.
It depends a bit on your age, but 150-160 sounds about right for the average 'cardio' zone. 170-180 sounds about right for the average anaerobic range. As noted above, heart rates are not always the best predictor of exericse intensity. You may want to look at the Rate of Perceived Exertion at www.sparkpeople.com/resource/fitness_artic
With the elliptical, the intensity depends very much on the combination of speed AND resistance. By using a low resistance setting, it is quite possible to cruise along at a high speed without much effort. And speed is something you can see what your neighbor is doing, but you can't easily see the resistance setting.