First: I am not a sailor. Sail boats usually have a lot of lines, block, cleats, jams, travelers and what not on their decks to control the boat and sail system. This looks like a cluttering mess on a deck. But, I have seen some sail super yachts with very clean decks. Wally, Sizzler daysailer and similar. I wonder how such a clean layout is done. I do understand that much is done with hydraulics or electric driven winches, but even those are not visible. so I guess there must be some clever way to hide this hardware (blocks, winches) below deck and out of sight. How is this done, are there special underdeck version of travelers and such?
Not everything needs to be located underdeck, often some hardware is semi-sunk in the deck, or grouped at a navigation/manoeuvring location on the boat. This can make it less visible. Even in more conventional non-luxury sailboats the fact that everything is neatly routed along the deck helps in reduce cluttering and not make the sailboat look like a man of war when you look at it (and there's a reason many boatowners are neat freaks, even if just when it comes to the boat) Some hardware designed just to be flush with the deck and the use of electrical components also allows less conspicuous placement of some equipment. Some components can easily enough be completely located below deck, like furling gear, and they can be also operated manually from above deck in case of failure..
In some solutions only part of the system is routed below, like the placement of the traveler tackle in the Farr40. Often whats routed below are just all the "ropes" and, wanting, this can be designed into smaller affordable sailboats (I suspect some small boat owners would not like to have to maintain such a system).
Its not just a matter of aesthetics, racing boats often use these systems to maintain a clean deck and lower the centre of gravity and their main drive is the performance of boat and crew.