you do exchanges with "real people", not with a service, so you get to choose from between different available deals and rates. The downside is that you have to find someone who is willing to convert the amount you are interested in, which isn't always possible.
And like Slax says, all all paypal exchanges are held for 7 days by a guarantor before the money is transferred to you - this is to make sure that enough time has passed for someone to report an abuse in case someone has hacked their paypal and made a transfer.