Hamilton declined to comment after the race. In hindsight he obviously knew the stewards were coming to some kind of judgement and didn't want to be seen to be contributing to the debate whilst the investigation was ongoing.
Fernando Alonso was inches from death as Grosjean's car flew over the top of his Ferrari. Hamilton, Perez, Alonso and Grosjean himself were all unable to carry on after the horrific pile-up.
The FIA took the incident seriously, saying:
"The stewards regard this incident as an extremely serious breach of the regulations which had the potential to cause injury to others. It eliminated leading championship contenders from the race. The stewards note the team conceded the action of the driver was an extremely serious mistake and an error of judgement. Neither the team nor the driver made any submission in mitigation of penalty."
Lotus' reserve driver, Jerome D'Ambrosio may drive for the team in Monza.
There have been plenty of dubious moves this season, mostly from Pastor Maldonado, but the Grosjean move at the start of the race and with the notorious Spa first corner approaching was particularly dangerous. The stewards have now sent out a signal that dangerous driving in f1 needs to be stamped out.
The last time an F1 driver was banned was Michael Schumacher in 1994. He was banned for two races for ignoring back flags at the British Grand Prix.