WordPress' searching capability is a bit mediocre at the moment. It splits up the keywords, digs out texts using SQL
LIKE statement, and returns all entries that match the criteria, in a reverse chronological order. Then the default template will display some of these entries, using the template function
the_excerpt(), which basically returns the first 55 words, HTML striped.
To have a more functional search, i.e. returning entries in the order of relevance, I think WordPress would need to either try to index the text (which is wha Search Reloaded plugin is about), or utilise MySQL's full-text search functions. Both would require modifying the database layout and change "the loop". Yuk.
To have a more meaningful result display, i.e. returning text snippets surrounding the matches, is however quite easy to achieve. Thus my Sunday evening's little project, "Search Excerpt" plugin that displays more meaningful result than the default first 55 words.