I am explaining by example:
A customer goes to the website and buys a service and opt for recurring payment. To complete the transaction, customer is redirected to the PayPal site. Customer does not have PayPal account and opt to pay via credit card. In such scenario is it possible for a customer to complete the transaction as a recurring transaction. If not then it is OK, but if it is so then later ON how customer can cancels this subscription as he has no account to log on to PayPal.
PayPal now has an add-on for Website Payments Standard called "Enhanced Recurring Payments" that makes it possible now to have recurring payments without making your customers signup for PayPal. It costs $19.95/month extra to use this. The add-on also adds a few other features, like Installment payments, and Automatic Billing.
Here's a link to their overview page.