I think the instrument definitely makes a difference. I'm not sure about THE DIFFERENCE. I've played a 1967 Martin OOO-18 for about 3 years now. The short scale length (24.9 inches) and small body certainly affected my playing and I've probably adapted my style to that guitar. The other day I acquired a slightly used Martin D-1R. I noticed an immediate change in my approach to many songs I often play. It is definitely a "bluegrass" guitar. It holds its own with banjo as far as volume goes without having to try to overplay it. At the same time, I've come to appreciate the old OOO-18 for the songs that are really suited to its tone and balance.
So does the instrument make the difference? I'd have to say yes. Some instruments just have the sound, the look, the feel and even the smell that enables a musician to present a song in his/her own special way. After all...isn't that why we play?

After a long (too long) absence,
Dave T