Yes and no. Parasites in the wild are controlled by factors not found in the aquarium. Different strains of fish are resistant to parasites--for example, rainbow trout are verys susceptible to whirling disease, but brown trout and cutthroat are not. The bigger factor is space. A parasite in the wild has a very slim shot at finding a host,let alone 2 or 3 at just the right times, so few survive. In an aquarium, especially for single host parasites like ich, the hosts are literally a captive supply, and almost every parasite will find a host. In wild populations, few fish will be heavily infested, and from some waters, none will be. For example, one local lake has lots of leaches--almost every fish pulled out will have a few of them. But, fish lice are seldom seen. Other waters, I've never seen a infected fish from them. Not to say they don't exist, just in much lower concentrations.
There is a lot of evidence indicating that parasites, along with predator/prey relationships, are a major driving force in evolution. Parasites are amazingly complex and effective--some so much so that they control/influence behavior of infected animals.