Is a credit card company required to have the funds on hand prior to offering you credit?

Not necessarily. They simply need to be able to balance their books at the end of the working day. They can issue a new customer a credit limit for immediate use - so long as they can balance any new 'withdrawal' by the end of the working day. Remember - you're unlikely to be their only customer. Existing customers that have borrowed on their own credit cards will be paing interest on their balances - so the company will always have the 'promise' of funds going back into their account to cover new accounts.