I love this thread, I've wondered this since GT 1... I just wish all the camera and head movement was in this view to show inertia better. That's on thing that the cockpit does well.
But there really is no substitute for a proper hood cam with a rear view mirror.
My real seating position is bolted to the floor board of my race car and I can't see the road in front of me... This drives 'normal people' nuts but its a trade off for a lower center of gravity... So the bumper cam is weird to me... The surface of the track is really the last thing you need to see on a racetrack... You would be surprised how much faster you are even in GT if you look up, but the bumper cam mixed with suspension dive, promotes a very false behavior/habit.
Try it, force yourself to look up more, try not to look at the track at less than 20 yards out, use signs and objects as reference, report back your results.
Riding curbs (mentioned above), and why they exist; most turning in a race car is actually sliding at a slip angle, drifting ever so slightly on the edge of mechanical tire grip. When you set up a turn you factor in where your going to end up based on entry, anticipating drifting to the outside. Its a lot like pool in thinking about where the que ball ends up so you have a good next shot. The idea is if you 'aim' to hit the apex you'll end up just slipping around it and its the first indication of where you're going to end up at your given trajectory.
Curbs are there because many other factors can change on any given lap and this allows for some degree of error correction. Of course more consistent drivers learn to use this and it's ok so long as 2 tires remain on the racing surface at once. This is also why tracks like Laguna Seca and Silverstone have 'sausage strips'. Laguna Saca has very extreme bright red sausage strips and aren't modeled in GT for some reason... (Its a shame as those are what give this track a lot of personality to drivers) But those are raised aggressively by several inches, and have claimed many a front end to the guy trying to eek out a couple tenths.
But what about those large painted areas found beyond the curbs on many European tracks? Those are open to interpretation based on regulation rules but many series still consider those the racing surface in events like DTM and VIR but they are not reliable to use consistently as they are often raised and slick intentionally, but they do promote aggressive driving and that's what the fans like. GT is very inconsistent about these as you can cut the corners at the end of spa and beginning if Mona pretty aggressively, but you can't run wide on Nurburgring GP... But again, those areas painted areas have several definitions depending on who you ask.