Though I can't say that the illustrator bent over backward to imitate reality here, it can be said that this is a clever way to sell Guinness. The portion representing the foam head gives this piece a nice sense of color balance.
A very classy design for a very well known company. The green border allows this logo to feel sunken in to the back of the design. Depth is a key factor in the success of this design. Shading and a consistent light source are also very effective.