Hmmm…I guess it all depends how the heating mechanism works. If you overheat the water for coffee, that’s normally A Very Bad Thing. The only exception is in making Turkish coffee where water is boiled in the process. Overheating your coffee will usually turn it noticeably bitter and rancid. Burnt coffee sucks, trust me. A similar thing happens when making green tea. Water too hot? Tea tastes like ass.
So overheating the water is a possibilty, depending on how these coffee makers work. The other possibilty comes from the water source. In my flat, the boiler is old and the water that comes from it definitely has a mineraly taste which the cold water does not. Coffee should be made with filtered water. Put some tap water through a Brita and then make coffee. It’ll taste much better since coffee is about 90-95% water, the rest oils. Yes, it makes a huge difference. The coffeeshop where I worked had a seperate, filtered water source for the brewed coffee and espresso.
Perhaps your boss worked in a place with an old water boiler or got some information passed on to him from somebody who once had a friend who had a friend who said hot water is bad for coffee since his hot water source wasn’t as “clean” as his cold water.