One driver was on the edge of the circuit (with a wheel on the grass ultimately, but could in theory have lifted to avoid contact), whilst the other driver was moving towards the edge without any consideration for the fact that there was already a car in the way.
Assuming that Grosjean's ban was for what he did, rather than just the resulting accident, then Alonso should be banned for one race. Consistency and all. In fact, given that the situation occurred recently (Grosjean), Alonso should have been more careful, so his ban should be two races.
Unless of course it's okay for Alonso to crash into people that are already on the grass, but not okay for Grosjean? Or it was Hamilton's fault for crashing into Grosjean at Spa?
Both incidents were almost exactly the same. It's just that Suzuka doesn't have a hairpin first corner, and Alonso/Raikkonen were on the outside, so it didn't result in a massive crash.