Now that you mention it, they do look dinerish. But the plumbing is on some other cars too just not as extensive. Another possibility: were those cars recently converted from gas to electric lighting, and that was the only place to run the wires?

Down at the end of the article, there are links to similar spreads on the SP station in LA and Union Station at its 75th anniversary. The SP station pictures are interesting - that must have been a standard design, because it showed up (in different sizes) in several places. The old 16th Street station in Oakland and the Sacramento station both resemble it, at least from the front.

And how times have changed ... everything built of brick back then, in Earthquake Country. The ATSF station article noted damage to the dome from the 1933 Long Beach earthquake - interesting that most of the stories about that quake don't mention much damage in downtown LA, concentrating (logically) on the much more spectacular damage closer to the quake's center.