The idea of keeping track of the sales receipts as well as the licenses themselves is ridiculous
You can't be serious. Not keeping track of what you legally purchase, as a business, is ridiculous. You have clearly never run a business of any kind. Of course you keep all the receipts, it's the law!, besides, not keeping them will cost you money since your accountant will not be able to deduct those expenses from your operating costs.
I did not say to not keep track of a purchase, but I did say that some purchases can be made for cash that can save money. All you have to do is write up the cash purchase on an expense voucher and submit it to accounting for reimbursement. I've done that on several occasions. There are vendors at the monthly flea market that will offer a 10% discount for cash purchases. Just be sure to check for the presence of the holographic CD/DVD and the presence of the license and legally you are good to go. If you buy the same product from a store you might pay many times that much.
When I say a lean mean startup, I mean exactly that. Linux is the way to go for 90% of the work, using Windows, properly licensed, for the few things that Linux does not do well yet.