For one thing, you have access to a harmonized scale in 6ths on the first and third strings with a combination of a straight bar and a forward slant of one fret (forward slant being that the nose of the bar is higer than the back of the bar). To get the same scale on G tuning you use a forward slant of one fret and a forward slant of two frets. I play far fewer two-fret slants, just 'cause they're so tricky to play in tune.

A nice thing about G tuning is that you have a sequential chord (135135) with no chord tones missing. This is also a drawback, because the overall range of the tuning is an octave and a fifth, while your tuning and D tuning have a range of two octaves (151351). I get far more use out of having the root on the first string. I hardly ever miss having a 3rd way down in the bass range. As a matter of fact, not having it is more of an advantage. Having 151 on the bottom gives me the ability to more easily fake a minor chord--or play one of the 3 minor chords possible by using an open string for the third of the chord (Bmi, F#mi, and Ebmi).

I've done lots of playing with country and bluegrass bands, and a lot of recording using D tuning. It works _very well_. The only time I will grab a G tuning dobro is if I want to get that Josh Graves sound on some classic Flatt & Scruggs tune--and if that's all you want to do, G tuning will serve you well. It's part of that sound. But I think there's a real "everybody does it that way so I guess I'd better do it too" aspect to the use of G tuning.