Well Phil,
Actually it has to do with taxes and the corporate structure.
The UP was incorporated in Utah
The SP in Kentucky and
The D&RGW in Delaware.
Delaware offers a much more favorable tax structure and corporate laws than does any other state. If you look, most major corporations can claim Delaware as their state of incorporation for just these reasons.
But if you want to construe it as a tribute to the D&RGW, have at it. For years the D&RGW was a pain in the tail to the UP and for that reason alone deserves a special place in history.
Rick