Our checkout combined with Authorize.net and your own merchant account would provide the same results. Keep in mind that services like Authorize.net and your bank will charge you monthly fees. That is one very nice thing about PayPal.
If you shop around you'll find that most banks will charge you around 27 cents per transaction, add in another 5 cents for authorize.net. Average in the monthly fees for the merchant account and unless you're doing a large volume or have a brick and mortar store then you can see why PayPal is the most popular choice.