Sounds like another fish story. The "floating feeling on cruise" is a function of damping - shock absorbers. Most cars are somewhat underdamped, especially in rebound, which can make them "float" over road undulations at high speeds.
Most Mercs, at least vintage models have excellent damping, but I'm not sure about the later models. Maybe they reduced rebound damping to cater to American customers who value a "smooth ride" over vehicle control.