Keep in mind this policy only applies to customers with unlimited data plans on the 3G network.
Verizon doesn't slow down data for 4G customers. This means that if you have an
iPhone 5 with 4G and
you live in an area where Verizon offers 4G LTE service, you should never have your data throttled or slowed down even if you use more than 2GB of data per month.
Why is there a distinction? The 3G wireless network as you note in your question is much slower. It's also much more crowded than the new 4G network. Since Verizon services more customers on a network that doesn't have as much capacity, there is more opportunity for congestion.
Verizon's 4G LTE network offers much more capacity than the 3G network. Think of the two networks as highways. The 3G network is a four-lane dual highway where traffic moves just fine during off-peak hours. But during rush hour, it may turn into a parking lot as too many
cars crowd the roadway. The 4G LTE network may be an eight-lane highway with four lanes in each direction. Because the road is wider it can handle twice as many cars. So during rush hour, cars are able to still move freely.
In other words, Verizon still has plenty of capacity on its 4G LTE network. The road is bigger and there are actually fewer drivers on it. Although that is quickly changing. In October, the company said that in September its 4G LTE network
handled 35 percent of its mobile data traffic. And that figure was expected to cross the 50 percent mark by the end of the year.