Comment on: "Band Filling and Interband Scattering Effects in MgB2: Carbon versus Aluminium Doping"

In a recent Physical Review Letter Kortus et al. claim that the observed decrease of $T_c$ in Al and C doped MgB$_2$ samples is mainly due to the band filling by the electron doping but for a fuller understanding of the different behavior of the superconducting energy gaps in Al and C doped samples it is necessary to also include an increased interband scattering for the carbon doped samples. We argue in the following that this latter statement is misleading and is based on the assumption that for carbon doping the two superconducting gaps merge near 10 % carbon doping: an assumption that contradicts most of the existing experimental data.