In response to your question: "Why a separate bank account?"
Because you can withdraw the funds immediately upon payment. (I do this with wire transfers too.) The better question might be: "Why withdraw the funds immediately upon payment?"
The answer is: Because Paypal will, and does, take back the money if there is a problem reported by the buyer. (No matter what you as the buyer says.)
Paypal is setup first and foremost to protect the buyers, and not the sellers. (They make the wrong assumption that the buyer is always right and legit, and that the sellers are merely capitalist pigs out to screw the buyers.) The proletariat must be protected from you bourgeoisie types of capitalistic, profit minded, pigs, as both Karl Marx and our president believe. ;-)
I suggest you check out this link and read through all the problems that using Paypal as a seller can get you into.AudioAsylum Search for "Paypal" in Shady Lane
This is not to say that Paypal is completely corrupt, they are not. In fact, I like to use Paypal when buying things, specifically because they make me the buyer their number one priority in protecting. (But I don't accept paypal as a seller, for the same reason.) As a seller I stand behind what I sell, (and I have ponied up money for items damaged in transit). But I don't want Paypal acting as a stooge for some scam artist trying to steal my equipment, (and hence my hard earned money).