This would really depend on the volume and average size of payment, considering for most smaller providers PayPal, GoogleCheckout, MoneyBookers etc provide the service for your customers and their details are secured and handled by a trusted third party for a small transaction %, however when providers are accepting larger payment for dedicated servers such providers are more than happy to dip in and use a higher % bracket or band at which point becoming PCI compliant is more appealing.

It's really a case of juggling the cost as well as the trust of a 3rd party VS doing it yourself and the cost involved.