It's not that simple as the roll pitch yaw. There is no way to tell the angle of an object with respect to the vertical up. Using accelerometer only works statically. If you accelerate, accelerometer no longer tells vertical up but off into the direction of acceleration so considering its reading to indicate vertical up is no longer accurate. In this case, the gyro axes can help to make the orientation more accurate. That is what I imagine.
There is no such critter as "static acceleration".
By definition acceleration is the rate of change of velocity.
In an aircraft one of the most important instruments is the "slip and turn" indicator.
With gliders where you are simple forbidden to have an HSI, Horizontal Situation Indicator, you simply should NOT get into a flight configuration where you will need one!
Most glider pilots use a simple piece of red wool with a small weight on the end.
In a "balanced turn" the piece of string or slip and turn meter will be pointing straight down, not at the GROUND, but straight at the floor of the cockpit.
If it's to one side your tail is "slipping" in that direction, how far it is off to one side is how "unbalanced" your turn is.
That's yaw and in a fixed wing aircraft it is the prelude to a tail spin.
Once in a tail spin, the wings stall and ALL other control surfaces besides rudder have NO EFFECT.
Without enough vertical stabiliser and rudder area, a tail spin is UNRECOVERABLE!
V tails in particular are a total prick to recover from a spin.
Most of the training from an unrestricted or "night/visual meteorological conditions" licence to an instrument rating, is getting the pilot to ignore what their inner ear is "telling" them.
With a ground vehicle yaw only happens when you are in a spin or starting to spin out in a drift.
I might have to put together a video illustrating what I'm talking about.
My UAV is getting a new tailplane and wing, as well as a SeeedStudio Mega!
I'm working out all the code for 6DOF and 9DOF on the ground because it is a much more forgiving environment to experiment in.