The only thing I can come up with about the Hydro is the write up for HD and it say they are commercial grade transmission what ever that means.
Like I said its not the quality of say the Toro or Exmark and I agree with you it's not consistent with what you get on other brand ZTR's for close to $5K but If he's buying it for $1800, would you think it's a bad price.
It seems to run along the lines as the rest of the mowers from Home Depot like the Stanley.