Actually that's not true. A lot of freelancers I know are very proud of and attached to the projects they work on.
Might be true for some others, like some of the overseas firms you'll find on elance who crank out insane amounts of code, but for individual freelancers my experience has been that they care a great deal about what they work on.
Freelancers are not employees. They're not attached to the business on a full time basis, and while they may get excited by the business and be happy to be working with the entrepreneur, in the end they are mercenaries.
Further, when the project is over and they walk away, the knowledge behind your product and technology walks away with them. This is true of employees as well to some extent, but at least with employees there's an expectation that they will be involved for a long term. For them it's not just another contract.
Contractors can be used to augment your development staff, but should never be your entire development staff.
Sure, you CAN have a success with a product built by freelancers (Digg is an example of this) but it is very, very rare.
No one is suggesting that potential business partners take each other out to the movies. But it's a good idea that they spend a lot of time together and get to know each other well before jumping into a partnership together.
That's why the analogy works. You don't meet someone at a party and marry them the next day. You shouldn't meet someone at an event and make them your co-founder immediately either.
That's what an analogy is. "a⋅nal⋅o⋅gy - a similarity between like features of two things, on which a comparison may be based"