Granite countertops ARE porous if left unsealed.
All natural stone possesses some amount of porosity. How porous your granite countertop is will depend on how it is finished, and how it is treated.
Polished Granite Is the Most Durable
Most granite countertops are polished then sealed making them nearly impermeable. Polishing the stone creates a flat, smooth surface that reduces the porosity making it more resistance to spills and stains. The addition of a top-coat sealer helps to strengthen its endurance.
Honed Granite Countertop Finishes
If you opt for a finish other than a polished finish, the surface porosity increases.
The honed finish granite countertop is polished to a smooth surface but not enough to produce a reflective surface resulting in a more subtle, natural looking stone appearance. This finish will be more porous than polished.