Reo-Coker and Gardner clashed on more than one occasion during a disappointing 90 minutes which produced few clear-cut chances.
Reo-Coker appeared to kick Gardner in the back midway through the second period but he stayed on the pitch before eventually being substituted as a tactical move by Villa boss Gerard Houllier.
McLeish said: "It doesn't seem that Reo-Coker and Gardner get on. I deduced that quite early.
"Nigel had a lash out and some referees might have interpreted that differently. He (Howard Webb) didn't see it as violent conduct.
"I saw Nasri at Arsenal when he kneed Liam Ridgewell in the backside in a similar fashion. I've seen them get sent off for that."
Birmingham also had strong first-half claims for a penalty when Reo-Coker appeared to control the ball with his lower arm inside the box but referee Webb waved play on.
McLeish said: "He moved his arm. It is human instinct to move the arm. But we've not had much luck with penalties for a couple of years and it was no surprise not to see it given."
Birmingham players lost their discipline after being beaten by a controversial spot-kick in the corresponding fixture last season.
But McLeish praised his players for keeping their cool in ending a run of six successive defeats against their local rivals.
He said: "I was proud of the performance of the players and the way they also kept their heads and discipline.
"Gardner was treading on eggshells after his early booking and it was another part of the learning curve for him.
"The last time we were here, we ended up in trouble. I told them to zip it up and not get involved with officials but still play with passion and we did that.
"We will take the point but one or two in the dressing room were disappointed we didn't take the chances we had."
Villa boss Gerard Houllier felt his side's extra-time Carling Cup performance against Burnley in midweek had an impact on their performance.
He said: "We lacked a bit of freshness, imagination and creativity. I think we have to take into account most of us played two hours in midweek.
"I'm happy with the effort and that we really competed in a tight derby.
"Maybe we lacked a bit of stamina but in the last half-hour we were better because we brought on fresh legs and maybe the best chances fell to Ciaran Clark and Ashley Young."
Houllier left £8m midfielder Stephen Ireland on the substitutes' bench and warned he must work harder at his game after preferring Clark to the former Manchester City midfielder.
He said: "Stephen needs to work harder. He played well at Chelsea but the way he played against Sunderland last weekend was not good enough for me, simple as that.
"He needs to work harder and needs to compete. It is a difficult period for him. We support and back him.
"We know he is a good player but he needs to work harder in games."
Source: Team Talk