The other half is that almost all of the binary formats can't be merged and so you need a mechanism to lock them to prevent people from wiping out other people's changes. Unfortunately that runs pretty much counter the idea of DCVS.
Don't their artists and designers use version control too? Maybe they just have one such person per team, or each person owns one file, or something like that. Hard to say.
Maybe it's like how I used to work on teams that never used branches - you have various problems that you figure there's probably a solution for, but there's never time to (a) figure out what the solution looks like, (b) shift the whole team over to a brand new workflow and set of tools, and (c) clean up the inevitable mess. So you just work around the problems the same way you always have - because at least that's a known quantity.
Perforce was always the gold standard for stuff like this. Did a great job at not only providing locking but stuff like seamless proxies and other solutions to common problems in that domain(like a usable UI).
This way you can look at both and resolve the conflict.
If two people touch the same file at the same time someone is going to drop their work on the floor and that's a bad thing(tm). You need to synchronize their work with a locking mechanism that informs the user at the edit(not sync) point in the workflow.