This is incorrect. PayPal Express Checkout and PayPal Standard both will require that you have an account, or sign up for an account to make the purchase.
CORRECTION: PayPal Standard does not require that a customer create an account when purchasing - sorry for the confusion. Either way, the following information still applies...
The bottom line is that if you want PayPal Standard, you give up some valuable features of PowerStore - which is typically not ideal. An alternative, which may not be perfect, but works well for many people, is to use the Express Checkout option.
If you are willing to give up those sorts of features (inventory control, order management, etc.) then you can go ahead and make the change. I would not suggest it, because i would prefer to have those features.
Express Checkout is definitely not perfect. However, if you take a look at the process, it is quite seamless for a customer. The account sign-up is created at the same time as entering their credit card details, and so making the purchase is quite straightforward.
The best scenario will always be to pay for PayPal Payments Pro and get all the features with local checkout. Obviously, this is not possible for everyone and a free solution is needed. The only free PayPal solution which will work perfectly with PowerStore is Express Checkout.