I do believe that forming words whilst speaking and singing are processed differently both physiologically and by the brain. Mel Tillis and Jim Nabors are typically given as examples.
Here Ozzy demonstrates...
Speaking Voice
Posture doesn't play a noticeable role during speaking.
Only shallow (chest) breathing is required to produce speech sounds.
Spoken words feel as if they originate in your mouth; you feel vibrations in the mouth and throat while speaking.
Words seem to leave the mouth on a horizontal stream of air.
There is no real sense of vibration or "tingle" above the upper lip while speaking.
The roof of the mouth is uninvolved or feels low and "lazy;" the jaw is often quite rigid.
Singing Voice
Good posture plays a big role in deep breathing; more air is needed to produce higher pitched, elongated words.
Deeper breaths (involving expansion of the belt line and and the back) are needed to produce singing sounds.
Words produced in your singing voice feel as if they originate in the area around your eyes, nose, or even forehead; you'll feel a sense of vibration in these areas more than in the throat.
Words seem to float into the head on a vertical column of air.
There is a real sense of vibration or "tingle" in the areas above the lips--such as the nose, forehead, or around the eyes.
The roof of the mouth is arched and raised, as if you're beginning a yawn.