OK, I see, I just ran a test with payments standard, and I do see the option to checkout with out a credit card, I was going from screen shots in the PayPal standard documentation which did not illustrate this.
So you are correct, with payments standard it is possible to except payments using credit card with a PayPal account.
Nonetheless, Paymwents standard is not integrated into PowerStore.
The main point here is that converting PowerStore to use payments standard:
1) is Not Supported.
2) Will break functionality such as storing the Information in the database and inventory control.
and 3) Not recommended.