@perspicacious01 As I understand, full text search would require much more resources than a simple hashtag indexing. On the other hand, knowing that hashtags are searchable, allows to write messages with predictable #discoverability. I mean that adding a known hashtag to a message will ensure that the message will be present in the "Hashtag timeline".
BTW in #AndStatus such "Hashtag timelines" (like other Search timelines) are the "first class timelines". I.e. you can sync and use them exactly like e.g. Home Timeline.