Just like the others have said, macbook is a Consumer laptop, meaning it for the most part, will run Consumer applications. So iLife, firefox, ms office are probably the major ones, and maybe logic express/ final cut express type of software. It is not meant for hard core gamers, video production types and such. That's what the mbp is for. So for the purposes that its suppose to serve, and applications that its suppose to run, the integrated graphics does a great job.
I know some professionals also use mb because of their size and the fact that their work don't need great 3d performance, but that's just a nice extra on the side. In general, Apple didn't design the mb to be a professional's laptop. It's designed to be my mom type's laptop. And honestly, she doesn't even know what a graphic card is. It goes to show how little it matters to an average consumer.
I know some professionals also use mb because of their size and the fact that their work don't need great 3d performance, but that's just a nice extra on the side. In general, Apple didn't design the mb to be a professional's laptop. It's designed to be my mom type's laptop. And honestly, she doesn't even know what a graphic card is. It goes to show how little it matters to an average consumer.