Civil airlines use newer aircraft because the fuel bill is cheaper!
Tri-motors are almost irrelievent these days with ETOP approvals, arguably the death of Lockhead and Mcdonald Douglas who had bet on tri-motors being the future.
This move by the raf maybe a good one if they dont arse about with them. As long as they are RVSM equiped they can deliver troops to somewhere like muscat with C-17s taking them direct to theater.
If no Mods are requird a good short term buy!
P.S. Sounds far to sensible though!