The statement from the RFL whilst accurate in itself (because the safety of players leading up to arriving & during a match has to be paramount) is massively hazy and ambiguous and open for interpretation.
If by making that statement they are hinting that somehow players from the 19s might get hurt because they aren't physically ready or that because Salford might not be able to have full use of the interchange system that players staying out too long might get hurt then that would be the biggest load of cobblers ever as reasons to postpone a match and actually contra to the operational rules.
What grounds could they postpone on the basis of player welfare, that the stadium is dangerous/unsafe to access, the pitch is dangerous/unplayable, floodlight failure with no guarantee of returning power, player death (abandonment), player safety from fans, no team/match doctor.
As for numbers, the 13/17 playing strength isn't even a requirement in the laws of the game, only if DURING the game a team goes down to 4 players are the officials allowed to use that as a reason for abandonment so the not having 17 players fit is just tough titty.
Section B2: Match Day Rules
B2.6
d) One of the competing teams is reduced to four players due to injuries and/or dismissals;
Far too easy as others have said to call a knock (Morely's ankle for instance) as being more serious, a stretching of the truth to garner an end result, happens all the time not just in sport but in life.