The difference is that the sport opened up a lot more to a wider variety of people (namely, women) in the second running boom, it became far more inclusive. It was no longer the province of chiefly skinny guys in tiny shorts, Oprah and her minions were now venturing to enter and finish marathons. So it brought with it a higher proportion of dilettantes with lesser degrees of dedication and drive. It's simply a natural consequence, it's neither good nor bad in and of itself. The sport is probably healthier for the sport, ultimately.