Unfortunately, and I say this with the utmost respect, your opinion just isn't terribly well informed in this instance.
The motor trade is a bit of an oddity, in the sense that it deals in very expensive consumer goods with proportionally expensive ancillary costs, coupled with oddly low profit margins. That R3k that you just want the dealer to absorb? Let's take an average month at a VW dealer, as that's what I'm most familiar with: that R3k will equate to anything between 15% and 60% of the profit margin on an average transaction. Sure, the odd Touareg will pay for a few registrations, but show me any business where one would even consider writing off half the possible profit on a given transaction because, hey, some bloke doesn't want to pay extra... and, for added fun, he has this odd idea that he is entitled to discount because he thinks paying cash makes him ****ing special.
The spurious analogies to chocolates and fridges above neglect another element of the equation: retail stores are supplied with stock in an immediately saleable condition. Do you think Makro might adjust their pricing a bit if they had to hire people to complete final assembly of their fridges once delivered? Cars are supplied to dealers, necessarily, in a condition far from roadworthy, because they are prone to spending months in stockyards before needing to be transported hundreds or thousands of kilometres to showroom floors. No non-critical fluids, no fuel, sticky-as-**** protective sheets on horizontal panels to combat industrial fallout, weeks or months of caked-on dirt, unadjusted control systems, various small bits of trim in little plastic bags in the boot... and, of course, unregistered.
People need to fix all these elements before you drive off, and you will pay their salaries one way or another. As has also been said earlier, your (in a general sense) smugness at not paying a R3k fee is severely misplaced - you just got a R3k smaller discount than you would have otherwise.