How is driving between cars, some possibily moving, ever really "safe"? All the car has to do, on either side of you, is move over toward you like 6 inches, and you get to become nice and cozy with the pavement.
Regardless of how safe I can ride my motorcycle, that doesn't mean somebody else can't ruin my day because of their carelessness.
Edit: Side note, I live in CT where people drive like fucking madmen. Just yesterday I almost got ran off the road by some old dude in a white VW rabbit. I had to look back as I merged onto the highway like 7 times to make sure he wasn't still coming at the same speed, which he was. I don't know how you don't see me, I have a yellow bike...
Also, that article you posted the verbiage from, talks about going on the "freeway" but that it's only safe at speed of "20mph". Who goes 20mph anywhere other than on super heavy congested roads? In which case, I wouldn't be on a cruiser/sportbike/any thing other than a moped, if I chose to be on two wheels.