I'm damned sure the lowered chassis GS has a low seat as standard. I have one. The seat has two positions. Actually, the seat has one position that fits either of the two positions the frame mounts offer.
Ackshurely, that may not be true. The seat on my low chassis GS looks like it's the standard seat, with a part number ending 2736 (and not listed on RealOEM). The BMW sales blurb says the low chassis bikes are supplied with a low seat. I have recently heard that it's not unknown for the factory to fit the wrong bits. A chum ordered a 1250 recently with the comfort seat. The seat was anything other than comfort and when he challenged the dealer, was told it was the correct seat. Turned out it was the standard seat (part number ending 2736) and not the comfort seat he'd ordered. He's since collected the correct seat for the dealer.