well, tracker vs smart search is like kernel vs some app
tracker is developed to listen kernel events and track down things, while smartsearch is totally non kernel, that's why it needs so much power to exists. that would be very reasonable reason, but it needs full reversing of smartsearch...to be confirmed.
smartsearch idea is ok...though, but not as this, not in user mode...it needs full access to hardware so it can implement indexing methods better and less demanding.
anyway, if smartsearch is using kernel mode to index data, then it's developed by someone i really wouldn't like to comment...