This is not correct. A transaction cannot be processed on the PayPal site without a PayPal account.
When Payments Standard redirects you to the paypal website, the initial page has two forms: one to login, one to create a new account.
you may be mistaking the form for creating a new account as the checkout form because it includes input fields for your credit card, but look more closely at the form and you will see two things:
1) The title of the Form is "Create a New Account"
2) There are input fields for entering a password and validating the password.
when the customer fills in this form, they are creating a paypal account.