He named 7 overseas players in the squad, now obviously you have contingencies but if he really think he's limited to 3 what's the point of that?
a) the total number allowed might change.
b) there could be injuries to other overseas players selected ahead of him (Quade, Kerevi, Foley etc.).
c) there could be injuries to domestic players in key positions that necessitates picking an overseas guy (say Frost, Rhodda, and Holloway get hurt).
Personally I don't see the cap staying at 3 for this RWC. You need Quade, Kerevi, Koriobete if they are fit. To leave one of them behind is bordering on unthinkable and obviously hurts the squad. Then you have Skelton, Arnold's, and Foley, who aren't as critical, but could easily be differences makers as well. I think Jones wants to win and has enough leverage to get what he wants.