Studies on Internet topology are based on measurement data. There are three types of Internet topology measurements using different sampling methodologies. This paper compares all of the three measurements together by examining their topological properties, in particular the recently introduced structural metric of rich-club connectivity. Numerical results show that, although having similar degree distribution, the topological discrepancies among the three Internet measurements are significant. This work provides a "graph-centred" analysis on the limitations of each sampling methodologies that are responsible for the measurement deficiencies. © Springer-Verlag Berlin Heidelberg 2005.