Example:
gis=> select osm_id,name,landuse from planet_osm_polygon where place = 'suburb';
182933675 | Seadale Gardens | (no name)
There is no corresponding point for this place way. However, many polygon places do have corresponding points:
gis=> select osm_id,name,landuse from planet_osm_polygon where place = 'suburb';
68692986 | Nunthorpe |
gis=> select osm_id,name,landuse from planet_osm_point where name = 'Nunthorpe';
osm_id | name | landuse
------------+-----------+---------
27648220 | Nunthorpe |
"suburb" is just an example here; the same problem occurs (locally to Yorkshire) with everything from "town" downwards.