paypal limits the account if suddenly a lot of transactions flow in (like it did on bitpay when they announced pre-order). even higher chance for a restricted account, if they try to withdraw some of or all the received funds.
when paypal limits their account, they request for a tracking number, since the payment was for "goods", which need to be shipped.
BFL won't be able to provide the tracking numbers for the transactions, so their money would sit for 6 months at least.
If I were BFL I wouldn't use PayPal for preorders either.
PayPal is also known for closing customer accounts with no explanation. I personally don't want to keep several thousand dollars in PP if they can close my account whenever they decide to do so. Bitcoin stuff sold for bitcoins.