I think the best justification for using scala is that on one hand you have a very nice language which is maintained by some very smart people and has a lot of nice things that are otherwise only available with ocaml,sml, haskell, scheme, or F#, and on the other hand the programs are running on one of the best just in time compilation virtual machines that exist. Thats a very very nice combo.

[note for clarity: by smart, I mean the maintainers/designers are folks with phd's whose careers are dedicated to understanding how to design useful/powerful programming languages]