You don't HAVE to add campden tablets if you pitch enough yeast. The idea being that your healthy and abundant yeast choke out anything else that could be in there. That being said, I have always used campden tablets in my ciders and perry. The end product tastes great to me, so I think of them as insurance.
My understanding that wild fermentation can make an excellent cider, but there is also a good chance that it will make a nasty cider. When Im fermenting 35 gallons at a time I am not about to gamble with a $100 investment.
Sodium Bisulfites have many uses in beer/wine making aparently: