Anthony, sorry, clicked on edit instead of reply,
I base my statement on actual measurements of the suspension travel. Reading the quote, it could well be an omission or translation error, or just wrong. It's easy enough to measure the front suspension travel on any hexhead. Put a tie wrap around the fork tube above the slider, push it down to the top of the slider, go for a vigorous ride and see where it ends up. Measure the distance between the top of the fork tube and the bottom edge of the tie-wrap and you have suspension travel. The rear is more difficult to do, and is better done with the rear spring off the shock and with a tape measure. It can also be calculated using the minimum compressed length of the shocks, which is a number available on most aftermarket shocks, and I've seen it somewhere for BMW factory shocks. If the minimum (fully compressed) length of a stock shock is the same as the minimum length of a standard shock, then the minimum ground clearance HAS TO BE THE SAME.
I believe that statement by BMW would be more accurate if it stated "Ground clearance is adversely effected, and it can be expected to have less ground clearance - except at full suspension compression - under many conditions." - that would be an accurate statement for BMWs lowered suspension design. The use of "ALL" isn't accurate. Could it be different on the GS? Mebbe.. haven't measured those.