It is kinda logical, since most racing cars can barely hold idle without someone massaging the throttle. Really, I didn't realise so many people expect these cars to behave like a road car on startup? Racing cars start rough, want to cut out on you and mostly don't even have a starter motor to start with - that's the wirring/buzzing/leafblower sound for ya: external starter.
And if a Countach starts bad, that's because it's a notoriously unreliable car. Try to synch six twin barrel Weber downdraught carbs and report back to me if it starts at all! Too bad you can't burn clutches in this game... the Countach would need a new every 3.000 miles if you're lucky.
Instead of whining about the startup sound (which is an actual recording, so no contest there) be glad they didn't include the ugly side of these cars in the game.