Importance of speed 6-7 discs
One thing I like about the discs Vibram is releasing is that they're working over the crucial speed 6-7 range. This is a critical slot, because it encompasses the true fairway drivers.
Here are a list of venerated speed 6-7 fairways that are available from Innova: TeeBird, Eagle, Leopard, Gazelle, Banshee
In recent years, Discraft has also had slow releases, but in 2012 and 2013 they came out with Zombee (speed 6) and Mantis (speed 8).
I think these examples illustrate the importance of that speed for many players. For newer players, it's their first driver that they can be consistent with. For more experienced players, it's the slot for go-to drivers in many situations.
The other speeds have a lot less 'classic' discs in them for each manufacturer, I think, because those speeds are more niche-oriented. Newer players are still figuring those discs out, whereas experienced players know what they want, and there's a lot more ways to handle those longer, more difficult shots.