You see it's hard for Collingwood.........how many did he need to hit to justify the decision to play him.....50? 100?
The thing is, and I'm only saying this from playing at Grade level (obviously the mindset in test cricket may be different)......when you've got the extra batsman at the expense of a bowler you're always thinking you need more runs than usual to cover for the part-timers that are likely to be required.
Add to that, the pressure on Collingwood HIMSELF to score runs AND the fact that he's batting in the tail (more or less) and it totally changes the dynamic and mindset of the whole side. Bowlers don't mind coming up against a batsman down the order when the tail is nearly exposed
Sure it's easy to look at that batting lineup at 0-80 and say....wow look how many batsmen we've got....but I can't remember ever taking advantage of it when I've played myself.
Having said that though.....sure Collingwood may come on and take a few wickets and justify his selection and sure he may score in the second dig but I'm sure the Aussie bats would be feeling more confident than if an extra quick was playing.
I haven't seen anything of Anderson in the last year or so, so maybe he wouldn't have added anything but they say he swings it and he bowls at a reasonable pace and that seems to have proven to be Australia's downfall.
Who knows......the result at the end of the day is all that counts so all this may be irrelevant.