One goal of KDE 4 was that Konqueror stays as the army swiss knife for power users (Dolphin never was intended to replace Konqueror). Konqueror uses the Dolphin KPart for the file management and this implies that the Dolphin KPart must provide the same features as Konqueror in the KDE 3 series to keep our promise.
For KDE 4.0 we could not implement all those features. This is mainly because especially the view parts had to be completely rewritten due to Qt 4's interview. But we are working hard to fill at least some gaps until KDE 4.1. One often requested feature was the missing tree view. Well it's back again:
It is turned off per default in Dolphin, but I think it is no problem for Konqueror users to turn it on :-) There are still some minor issues when reloading views (e. g. the folders get collapsed again), but they will be fixed until the KDE 4.1 release.