David Platt: FA had to let Sergio Aguero off
Aguero launched into an ugly foul on Luiz towards the end of City's 2-1 win over Chelsea at Wembley Stadium on Sunday in their FA Cup semi-final.
However, because referee Chris Foy witnessed the incident, awarding a free-kick against Aguero, the Football Association could not reassess the tackle using video replays.
"I wasn't surprised, based on the rules that the FA have put in place," Platt said on Tuesday.
"If the officials have seen it and the precedent has been set, I am not surprised. The rules are the rules. We don't make them up, we just adhere to them."
Platt denied that Aguero was fortunate, saying: "I don't know whether it is a bit of luck. What is luck? I'm not sure really. The situation has gone. I am not surprised that he got off, because the officials saw it."
Meanwhile, Platt says City are focused on finishing the Premier League season strongly.
The reigning champions face Wigan Athletic on Wednesday night in the league, but with leaders Manchester United 15 points ahead, the defence of their title is all but over.
They still have a chance to win a trophy, when they face Wigan again in May in the FA Cup final, but Platt says the focus must be on the league first.
"I don't think the pressure is off because it is still on to win matches," he said. "The pleasing thing is that in the last two games (Manchester United and Chelsea), against very good opposition, we have performed.
"Rather than dramatise the situation, it is about finishing the season as strong as we can. Hopefully we can win the FA Cup. We still have to play a good team."
Micah Richards could make a return to action at the Etihad Stadium on Wednesday as he continues his recovery from a knee problem that has kept him out since October.
The England international has made just four appearances this season.
"Micah has been training with the team for 10 days, two weeks, and he has played a couple of reserve games," Platt said.
"He is available for selection. Whether he would get through 90 minutes, I don't know, but I would hazard a guess he will be involved in the squad. It is pleasing to have Micah back."
David Silva remains doubtful, however, having missed the Chelsea game with a hamstring problem picked up in City's 2-1 win at United last week.
"I think if we had pushed, we probably could have got him ready for Wigan, but it would be a risk," said Platt.
"We will probably be pragmatic and think (he will need) a full week's training under his belt. If the game at the weekend had been the last of the season, we might have taken a risk, but it would be a big risk. If he does play against Wigan, the weekend becomes a bigger risk."
Despite the fact the sides will face each other again in the cup final, Platt believes the clash with Wigan will not be similar to the Wembley fixture.
"Each team has four or five games before the final," he said. "Four or five games is far too much to have a correlation. We will have them watched and analysed. From May 1 we will have them analysed again."
Related Manchester City News