The logic to launch the search tool (from bug #497802) is odd. The logic is:

  if beagle-search is installed, launch it;
  else if tracker-search is intalled, launch it;
       else launch gnome-search-tool.

This is odd 'cause:
  * we have to change the code in order to add different/new search tools
    or change supported if they will change name
  * the if .. then .. else don't allow users choose the tool

While you can see this is an uncommon case, we could have systems where both beagle and tracker are installed (in the end this is UNIX, different users on same machine using different software). The logic isn't user configurable, so on that systems users can choose trackerd to index their data, but pressing the search button they will always have beagle-search tool.

Another example could be systems where the daemon is installed, but not the search tool (this is a working scenario too, 'cause you can still use Nautilus as search tool to interact with beagle and tracker).

Finally, please note that some (corporate) installations could have their own custom search tool, to search on shared databases, not in local files. A well behaving desktop should help this scenario, not lock it.

PS yes, are bleeding edge scenarios, but I'm advocating my patch from bug 491647 :-)