There are technical regulations and sporting regulations. I'm not very familiar with IndyCar anymore but my feeling is that F1 got stricter on technical regulation but IndyCar is even stricter: only one chassis and more standard parts. However F1 sporting regulations seems to be tighter. The classic clash between Villeneuve and Arnoux in 1979 would be unthinkable now. Not only they would be black flagged and stopped for a GP but no driver would even think about doing those kind of overtaking attempts.