Remember, 3D printing is already 30 years old. It has only had this spurt of innovation because a patent ran out and people started racing to make a cheaper printer.
I work with a $10k printer, bottom of the line for Stratasys, and a $400 printer from Printrbot. Their output is different, but not 25 times better.
This is very hot technology. Moving faster than anything before. People compare it to home computers and 2d printers, but there is something new happening here. It is the acceleration caused by the internet, specifically open-source hardware and software, crowd-sourcing and crowd-funding.
I think that Moore's Law is an understatement in this case. I would say that I have already seen a doubling cycle that is close to 6 months.