I think the main difference between HO scale modelers and 3-rail O scale modelers is the difference in the backgrounds and mindsets of these two segments of the hobby. There is a philosophical difference in the mindset of the two different groups.
HO scale modelers often try to recreate reality, modeling a particular scene from the real world down to the last detail. Operationally, most HO scale modelers try to operate their railroads prototypically, using single-track mains with passing sidings, establishing producing and consuming industry pairs, setting up some kind of car routing system for switching cars, using prototypical signal systems, a dispatcher, etc. For the HO modeler, running the railroad is a very active thing, where each engineer/operator is deeply involved in running his own train, obeying the signals, and doing whatever switching is required on his switch list.
The history and background of 3-rail O scale is very different. This segment of the hobby grew from the simple loop around the Christmas tree. Noted 3-rail modeler Bill Bramlage coined the term "Loop Runner" to describe the multiple concentric loop type of track plan that dominates in 3-rail O scale. For the 3-rail O scaler, operating his layout is a more passive activity, where they get several trains running on the concentric loops and just sit back and enjoy watching the trains run.
Neither way is "right" or "wrong." It's just two different ways to enjoy a great hobby.