But what would make Anakin killing him after he killed Ahsoka different? At this point Maul has taken more from Obi-Wan, so if anyone deserves to get revenge it's him.
Because revenge is not the Jedi way. It's one of the reasons Lucas wisely chose to rename Episode VI from Revenge of the Jedi to Return of the Jedi.
I could see Obi fighting Maul and ultimately taking him into custody or Maul somehow dies of his own accord, but the idea of Obi killing Maul in revenge for Satine doesn't feel right. Plus it goes against the whole Jedi detachment thing.
Anakin killing Maul makes more sense, especially if Ashoka is his victim, because we have seen Anakin kill in anger over a loved one before and we know what his attachment to Padme will lead to in Episode 3. Anakin taking revenge just puts him one step closer to a complete embrace of the dark side.
Plus it would might answer some of those Vader v. Maul debates.