You raise a good point Stilton, but as I previously mentioned, any aircraft design needs to balance design characteristics to best meet the required spec. Every design feature carries a benefit - and a penalty.
I agree with you about the benefits of leading edge slats. I have sampled these benefits myself operating the Falcon 900, especially when landing on short/wet strips when we had surprising short(er) field performance. We used to contrast this performance against that of compatriots in the smaller/lighter CL604, which had no LE devices. We held that the LE slats were the key to the performance difference.
However: the incorporation of leading edge devices into a wing takes up space that robs you of fuel volume therein, and requires the carriage of additional hydraulic/electrical services for operation and more complicated ducting for leading edge anti icing. This all requires a tradeoff in available payload or fuel load, and more complicated systems where things can go wrong. These offsets might have been undesirable in the eyes of Gulfstream's engineers, assuming they were aiming to reduce complexity and maximise burnable fuel capacity.
There may well be other reasons why there are no slats on a Gulfstream wing. If so, I share your interest in learning why.
Are they hanging on to the GI wing?? Funny guy - or a typo! But maybe they are just exhibiting typical conservative design philosophy, slowly evolving over time with experience and experimentation. Boeing did the same for years, sticking to what they knew, but producing rubbish wings until the 777. If you ask Dassault, the reason why the 777 wing was a significant improvement was because Boeing started using Dassault's CATIA CAD/CAM systems.
