If an SDE point layer is created in ArcCatalog for the Oracle Spatial format, the point coordinates are stored in the SDO_ORDINATE_ARRAY instead of SDO_POINT, even though the featureclass has no multi-part point features. This is because ArcGIS adds Z and M support to layers by default. The M support forces the point storage to the SDO_ORDINATE_ARRAY.
However, if the SDE point feature class is created for the Oracle Spatial format using the cov2sde or shp2sde commands, then the point coordinates are stored in SDO_POINT.
This has been fixed with ArcSDE 9.2. When a point layer is created using ArcCatalog, ArcSDE 9.2 now stores single-part X/Y and X/Y/Z point shapes in SDO_POINT.