Experience with freight operators on road and rail in Australia has shown that retaining elements of old branding is actually a good thing, even before you get to the issue of the paint job and whether it's worth taking vehicles out of service for non-essential maintenance. If the long-term big-ticket customers are satisfied with a freight company, then any other changes (including branding) in the wake of an acquisition should go as slowly as possible to try and convince them all that's changed is the ownership.
If the old outfit was a disaster that was purchased just to inherit assets and perhaps a few long-term contracts, then just about everything has to change all at once in an effort to convince customers the new company was not linked to the old. This might even need to go as far as shuffling around staff in a major restructure just to make sure that even the people the customer comes in contact with are all different.
As far as I'm aware, EWS had a pretty good reputation so DBS have a lot to gain by trading on that EWS name. That's even before you consider the operational implications of taking vehicles out of service.
It's different for a new company trying to win new business. For an example, Freightliner Australia has two contracts currently, operating coal trains for Xstrata using new-build wagons and XRN Class* locomotives that are owned and liveried by Xstrata, and also hauling daily trains of containerised cotton. The cotton trains use four leased locos currently, two of which have received PowerHaul-style livery (they operate in pairs, one in Freightliner Australia livery and one in standard CFCLA) to try and get a bit of visibility for the company, while that's not an issue for the coal side of things where it's a pretty closed system.
* New-build and rebuilt locomotives are classified by both type and owner in one code in Australia, even if they are the same model as those used by other owners. This can lead to nearly identical locomotives being known as many different classes, like the current C44aci built by UGL Rail which is known as the 92 class, AC class, 6000 class, XRN class, ACB class, CEY class, CF class and GWU class! It's really helpful because it can help you pick out odd workings without having to look up numbers.
Yes because the 37's were some of the first loco's they repainted, hardly saw much mainline use in their new livery before they were eventually put into storage in March 2010, as DB Schenker don't want to use them anymore. Meanwhile their main fleet of 66's and 67's, as well as the 60's are still in the slow process of being repainted/rebranded years later. Any logic there????
I can see two perfectly logical reasons.
1. The 37's repainted first could have been done as part of trialling the new branding, the idea being to use locos already used less intensively just in case the new branding was a failure. Backing up this theory, if the new branding was a rampant success then those Class 37's wouldn't be stored (because business would be increasing) and the rebranding would have been hurried up.
2. It could also have been an accidental move, painting the locos as they come in for heavy maintenance. Obviously the worst clapped-out relics would be the ones most likely to see some unscheduled heavy maintenance (and hence the paintbrush) the soonest.