Ì think Yamaha are being clever. The original FZ6 was to many, a bike that had unique looks.I think that single prism headlight is fugly. Fugly on all those bikes you metion. Looks too "transformerish" to me. Kinda neat and wierd looking, but not something I'd want to look at day in and day out, when transient style has moved on to some other bike component.
I've heard it put forth that dual headlights are bad because they can be mistaken for a car that is a long ways away rather than a motorcycle that is close with two headlights near each other.
These pictures are artistic renderings of what they speculate the FZ8 will be. These images are quite a bit older than the FZ8 announcement and should be disregarded.
This is not official, but interesting nonetheless, from Top Speed.com
2010 Yamaha FZ8 rendering - Top Speed
Another "best-guess" / "what if" picture. I don't care for the "transformer" styling, but the mechanical bits I see, I like.