Double walled mugs do keep coffee hotter.
The double wall construction of the mug helps to keep heat in the coffee mug so it stays hotter longer.
Insulated mugs also help to keep coffee hotter and for longer especially when it has a lid to help retain the heat of the coffee.
The pocket of air between the glass keeps your drink hotter for hours longer than in a regular mug.
The insulation works in reverse too.
Unlike regular glass, heat can neither escape, nor enter easily, so your chilled iced tea will remain refreshing for far longer on a hot summer's day.
When compared to glass, ceramic loses heat at a slower rate as conduction occurs slower in these mugs.
Since ceramic is more porous than glass, it retains heat better and your coffee stays warm for a long time.
I prefer ceramic mugs when I want to drink the coffee pretty quickly but when I drink coffee such as while driving I like to have an insulated coffee mug with a lid.
The lid keeps the coffee hot longer and keeps the coffee from spilling as well.