[1] Photographers don't camp in the press box. At a lot of venues (primarily football though) we aren't even allowed in the press box.
[2] Moving with huge telephotos isn't difficult. Take golf for example, that involves the same if not more kit than football, and it involves moving, a lot. At an estimation, about a round and a half of distance (27 holes) but this could be more or less depending on how lazy or proactive you are, and more importantly how the day is shaping up.
[3] You are right in that we rarely move for football. Penalties are one of the exceptions, and at half time. This is quite different from an affirmation of this "find a good spot and stay there" advice however. After all, how *do* you identify a good spot in football? That depends totally on what happens on the pitch, and as I pointed out in that thread, if you know that, then you should be at the bookmakers on the way and wouldn't have to take photos for a living. You can be at your "best" spot, and everything can happen at the other end of the pitch and you'll get sod all good.
Note also I did bring up advice not to chase the game, which is generally largely true because it more often than not bring more harm than good. So if you're plonked and a goal goes in at the other end, don't move. I wouldn't move if it was 2-0 either (due to a variety of reasons I won't go into here, but this is where experience comes in), and only very very occasionally if it was 3-0 or more. The one exception is if there is a story and it goes from being 2-0 to 2-1 and you'd be at the wrong end of the pitch for a potential equaliser, taking into account whether there is a long time to go in the game or not.
This is totally not the same thing as, if you find a good spot stay there. And in many other sports where the action follows a more predictable pattern, the advice could be, if a spot's not working, move. Which again, is very different from find a good spot and stay there. Also, get your shots, and then move and get something different.