Exchange points are not the be-all and end all of peering. They are a mechanism to allow the costs of a physical connection to be shared among multiple peering relationships, the downside being that you have to pay for the exchange points switching infrastructure. So low traffic peering relationships tend to go via exchange points while high traffic ones tend to go via dedicated private links.
There seems to be a big difference in attitude here between the US and Europe. The big access providers in the US tend to be very monopolistic and have the attitude that peering with "little guys" is giving away for free something that they could be charging for. In many cases those big access providers are also teir 1 transit providers.
On the other hand in Europe there is more competition among ISPs and the individual access providers are generally smaller and have to buy transit to reach large parts of the internet. The result is that there is more incentive for the access providers to peer directly with the content providers and internet exchanges flourish.