I am not sure I'd agree with that - at one point Salesforce tried to buy my company, which was a best-of-the-AppExchange partner, and their justification for their (very) low offer was "that's what it would cost us to copy you". We sold the company 2 years later for 10x their offer, without a ton in the way of new revenue (our AppExchange ranking mysteriously tanked after we turned down their offer).