Some of the longshot biases still exists and can't be removed due to technical constraints on the platforms. A lot of times there is a minimum contract price, which effectively means the probability of unlikely events cannot be modeled as lower than 1% or 0.1% or whatever. But there are contracts for events much less likely than that.
There are also issues with the time value of money for long-shot events. Someone has to be willing to buy a share of "No", and if that works out to a return lower than the risk-free rate (eg. buying t-bills) there will be no incentive to take the "No" position. That makes anything roughly under 3-4% per year pretty unreliable.
