Expedia Fiasco: No Invoice for Online Booking

I booked a hotel through Hotels.com and was surprised to learn that they don't provide invoices for online payments, only receipts. Their excuse is that they're an American company affiliated with Expedia. They also claim to have this information on their website, but as a customer, am I expected to comb through their entire site before making a purchase? This is unacceptable! As a customer, I have a right to receive an invoice for any purchase I make. This is especially important for business travelers who need to expense their travel costs. I demand that Hotels.com provide me with an invoice for my booking and make it clear on their website that they don't provide invoices for online bookings.