One of the fundamental parts of paypal is the ease in which a transaction can be reversed if the customer is not pleased. Bitcoin transactions are irreversable. Many websites that currently accept paypal may be cautious about this. So that means Paypal will have to take the heat if something goes wrong in a transaction. Something I don't see happening.
The fiat payments are usually not reversible either but it's paypal's system that is the weak link. Paypal doesn't actually take the money back out of your bank account they just minus the balance from your account and then you owe them the money so they essentially take the heat until you pay back. If they handled bitcoin payments it would probably work in a similar way. Either that or they will just hold the money as some sort of escrow until the transaction has been successfully completed.
Actually it does. I sold multiple items on eBay and some buyers submitted a claim that the item was not as promised or not as delivered. Immediately after the claim was filed, the transaction that put money into my account was instantly frozen and I was not allowed to access the funds. When eBay took support of the buyer, the same transaction was reversed.
PayPal can always act as an escrow service. But the money would be held for an enormous amount of time and buyers would have to send some sort of conformation that the item is as described and that they are satisfied with it to prevent a chargeback. Something that doesn't really seem realistic in the business world. Also, when you reach a negative in a PayPal account, youre more or less going to pay up since a typical PayPal account is very transparent. Bank accounts, credit cards, even SSN numbers are linked to peoples accounts. You can't just abandon the account and expect to start a new one. But what about bitcoin? Really the only information you would need to put up is your bitcoin address. You get debt in a bitcoin PayPal account its no big deal. This is why PayPal would probably request you link a lot of personal information in order for you to buy stuff with btc. Something a lot of bitcoin users may not be all to happy about doing.