I'll give it a shot....
The pace car comes out and the leader will be the first car that the pace
car "picks" up, i.e. the pace car will pull out in front of the leader after
you have taken the caution
Well, not sure if this is the real reason, but here is my guess. If you
were at a large track, like Michigan for instance, and you knew that the
caution was coming out and the pace car had just picked up the leader, you
could conceivably hop onto pit road, make your pit stop, and then get back
out on the track before the pace car gets back around to the entrance to the
pits allowing the leaders to pit. This would give a large advantage to
someone at the back of the pack, allowing them to then pass all the leaders
while they pit since he had already pitted as the pace car picked up the
leaders. Probably not the right answer, but like I said, that is my guess.
Well, I have found this to be one of the few complaints that I have with the
game, in the fact that with 43 cars to keep track of, sometimes the game
gets a little confused during pit stops and you may get hosed due to a bug.
The rule of thumb in real life is the first car to cross the white line at
the exit of pit lane gets the position. Also, if the train of cars that did
not pit is still making its way past the pits in real life, the cars exiting
the pits are held by a Nascar Official untill all the cars that remained on
the track have passed. The spotter may be instructing you to let the people
still on the track by you to simulate this. Perhaps not, but again, my best
guess.
Hope I helped and didn't confuse you more.
Kinny