It has the bandwidth of PCI-E, doesn't mean it's actually connected via that port. Even so, you can easily have a soldered connection of PCI-E on the logic board.
In any case, your video card is soldered on. That goes for all the Intel Mac Laptops
Just to add to this...
That goes for ~99.999% of all laptops sold. Very few have swappable graphics cards, and even with the ones that do (heavy gaming machines, a fractions of Alienware and the like), the upgrade choices are virtually nonexistent/very slim.
i wouldent go as far to say 99.999 but more like 85%
alot of dell inspirons have seperate video , most xps's also.
the upgrade paths are very limited.
soldering on board offers many more features and a cheaper production.