Ultimately, these deals are subsidized by people who get charged with massive deferred interest payments because they don't plan properly, and that sucks for them, but as you say, it's a great way to start experiencing the benefits of a purchase instantly.
Even better is to use the financing opportunity on something that makes money. I've furnished apartments using 0% financing, and I'll get anywhere from 50%-100% increase on rental income for a furnished apartment - while paying no interest on the loan! It's like putting extra money in your pocket every month for free.
Indeed, and it's important to point this out to those who insist "Average Joe" doesn't benefit.
Three of the largest investments people will make in their lives are 1) their home, 2) their education and 3) their vehicle. All 3 are generally financed, and financing rates are at historic lows.
We've paid off Couches, A refrigerator, a new Sewer Drain, and several other things (a nice Kitchen Table most recently) this way. It's not as good as saving for it, and getting a few dollars of interest, but that's a marginal gain anyway.