1. You can still have a cylinder stat.
2. As it does on a gravity system with a cylinder stat.
3. Also can be done with a gravity system.
4. Not if there is a cylinder stat.
All true of course. But I think you misunderstood why I said these things. So my apologies for any confusion caused. Of course it you fit thermostatic controls many of the advantages can be gained added to a gravity system, but the question was raised after I posted about a system that was an ancient gravity hot water system that had never been upgraded to have anything other than a room thermostat and that its owner would have done better spending his money upgrading the hot water control rather than on a Nest.
With a gravity system without thermostatic control whenever the timer is on, the boiler will continually fire up even when the hot water cylinder is hot. So the pipes, boiler etc will loose heat to their surroundings, also the cylinder will get hotter than necessary and add heat to the environment.5. Why is less heat emitted to the environment.
The circulation of the water through the system is much slower with gravity. Prior to converting mine it took nearly an hour to reheat the cylinder, now it's less than 20 minutes. Maybe it's a better cylinder but I can only speak as I find.8. So it is often said, but how?