Apple's target customer doesn't need a graphics card to do anything more demanding than video editing. It's been probably at least 7 years since you could get a Mac with anything like a top-of-the-line graphics card. Are there potential customers that Apple is not grabbing by not having a high-end graphics option? Sure!

But Apple doesn't care...

The thing about Apple is that, unlike almost all of their competitors, they really don't care about a "Mac in every home". They'd much rather target specific slices of the market where they can excel and make a lot of money (think BMW, not Ford).