It could also serve to protect neophyte project originators who have no clue as to what it takes to get a hardware project from a rendering or a garage prototype to a real finished product.
There are a myriad of technologies available today to produce very high quality prototypes that look like the finished product. Forcing project originators to show an actual product rather than a rendering will simply force them to make the time and financial investment to get the project to a far deeper level of completion and really think it all thorough.
If someone will not take the time and spend the money to put together a prototype that is a real representation of what it is they are proposing I don't think they belong on Kickstarter.
I would imagine that it would still be OK to show renderings and animations so long as the actual physical product is shown as well. The reason I think this is important is that this can also show supporters important details that may not be evident or easy to demonstrate with actual products. For example, animations could show internal mechanism and how they work. 3D renderings could show ideas on variants or configurations for backers to discuss and provide feedback for.
I have a couple of projects that have been slated for Kickstarter for months. I've been too busy with work to really get to them. In both cases my approach has been to fully develop the items to the point that they are basically ready to manufacture. The Kickstarter push would simply serve to gage interest and pay for tooling and other NRE's that would make it possible to fabricate the items in reasonable quantities at a decent cost. Of course, I've been in product design and manufacturing for a long, long time so I tend to be very realistic about what it takes to get something done. I've seen projects go on Kickstarter that would not have a chance in hell to be completed at the requested funding level. Not a good thing.
Above all, what this indicates is that Kickstarter is watching and listening, which is excellent.