Were YIR and VYK the only two aircraft heading for ADL that morning? If not, what happened to the others? Did they carry alternate fuel just in case and then successfully diverted to their alternates?
Where I fly, we always carry an alternate as well as 45 minutes holding fuel, even if the forecast doesn't require it. It's pretty much standard policy for airlines in this region to do so. If carrying additional fuel made such a huge impact on the airlines' bottom line here, I'm sure they'd stop this practice, but they don't so I guess they consider it to be better safe than sorry.