To be fair, PayPal doesn't force you to use bank transfer. They default to bank transfer, but you can always switch to credit card per transaction manually. I do that hundreds of times a year because I never ever use bank funding through PayPal.
Second, your situation is a tough one for PayPal to protect against. On the other side of things, as a recipient of funds, I wouldn't want a buyer to be able to dispute a charge after the fact on the basis that they typed it in wrong. Non-delivery is one thing, but typos are a different story. Again, to PayPal's credit, you have to go through a few steps of confirmation before a payment is sent. You DO have a couple opportunities to double check the amount.
Finally, with payments by CC, you can, as far as I know, start direct chargebacks if PayPal doesn't help you. PayPal doesn't like that, but your CC issuer will typically help anyway.
I here what your saying but what if due to some typo you meant to pay $100, but the typo was $10,000.00 so your just out $10,000 due to a typo? You can't believe thats fair? If that really were to happen you still have no recourse through Paypal. A CC company would never allow this.