I don't know if it is still the same, but the last advertisement I read on it was that you had to buy a super duper Acrobat Pro 3D to be able to create those files, though they are admittedly readable by the regular Adobe Reader that comes preinstalled on most computers or free for download.
It's kind of a wash... DWF is free to make and free to view, but the hurdle of getting random folks to go and download and install something off of Adesk website is pretty big.
Adobe, you have to pay like $700 iirc for the version of Acrobat that will make the 3D pdf files, but you get the convenience of being able to send them out to anyone and everyone with no worries.
But I guess if you're buying a $450 Acrobat Pro, another $250 could be worth it for that... I'm pretty sure Adobe put their research into finding out how to make money but still remain competitive or even ahead of the pack...