"It's a commercial decision of enormous magnitude. The attendance at the British Grand Prix would be severely affected by the fact Ferrari are not allowed to race.
"That is against the promoter, who has nothing to do with what happened in Austria."
Stewart admitted he was surprised by the events late in the race.
He said: "I was very disappointed and shocked by it because I really did believe Rubens was going to win the race and justly so.
"I just thought it was a complete anti-climax to what was actually an exciting grand prix."
The former Formula One team owner criticised Schumacher for orchestrating a "pantomime" performance on the podium - and claimed the German could have ignored his team's instructions.
He said of the podium fiasco: "This really was a mistake and I think it was a bit of pantomime in which everyone felt embarrassed about.
"Rubens was pushed into a position he did not want to be in. The manner in which it was all conducted was very embarrassing.
"It didn't look good for motor racing.
"Rubens drove an impressive race and it was a PR blunder more than anything else.
"Michael could easily have disregarded the instruction.
"He has more power at Ferrari than any single man I have ever known in all of my career in motorsport as a watcher of Ferrari.
"It could have been altered by Michael's personal initiative. He could have said it on the radio."
