Why landuse, and not surface?
Text removed from article: Often, if the area would no longer be actively maintained as grass, it would turn into some other natural feature; most likely into a natural=heath or natural=scrub. Likewise, even though humans take care of the landuse=grass areas, these areas are mostly not used by humans for anything other than growing said grass. Therefore, using the landuse=* is, if not justified, at least not wrong, even if it at first seems out of line with the other natural=* and surface=* uses.
I have copied this text here from the main page given that it is primarily a discussion about the tag and not of great relevance to someone wanting to use it. PeterIto 22:23, 1 June 2011 (BST)