KayPam,
Even in water, a fluid that's almost uncompressible, sound takes time to travel.
That means the bulk modulus
K is finite. Increasing
K results in higher speeds. In other words for an acoustic wave to have a finite travel time the volume of the material must change. The more pressure that is required to effect that change, the higher the speed.
In an incompressible flow (and medium)
K is infinite which means the propagation speed is infinite, in turn reducing the Mach number to zero for all speeds.
So basically we have air at low speed : it's almost uncompressible so we can use Bernoulli's theorem. It is a tiny bit compressible so we can use the sqrt(gamma R T) = LSS formula. If speed increases, the LSS formula becomes "more correct" (according to you, you still have to explain why it would less correct at low speeds), but Bernoulli becomes less correct.
Assuming an incompressible flow at low speeds is reasonable because compressibility effects are negligible while more accessible equations describe flow behaviour very well. From a rational choice perspective the fidelity reduction is rewarded by more tractable mathematics so that the simplifying assumption is rational. In the same vein it would be irrational to introduce a Mach number to most incompressible flow treatments.
But in any case, nothing prevents the engineer from performing computations that do not make perfect physical sense. One wants to compute a mach number as TAS/sqrt(gamma R T) ? No one can forbid him to do so.. Maybe tell them they're wrong but nothing more.
To ensure consistency such a Mach number would need to be qualified as an artificial one. What would be the practical application of such a number?
Because except by using wrong formulas, I don't see why this 0.94 thingy would be required.
The factor in the question was irrelevant but there is insufficient information for us to determine why it was given.