Carb Heat and Lycoming Engines
It's because the spider duct that connects the carb to the intake runners going to the cylinders is cast into the oil sump and the carb mounts directly to that. So the carb gets a lot of engine heat that warms the carb body by conduction. Also, it's getting radiant heat from the sump directly above.  

On Continentals the carb is insulated from the engine by its mounting and location relative to the sump.  Continentals without pressure cowls like J-3 Cubs are the worst for carb ice formation.

Carb icing is relatively rare on Lycomings but is still possible if the conditions are sufficiently favourable, so you still have to use normal carb heat protocols.