No matter how good a site is sometimes it is just not possible for it to be NO.1 without a great deal of expense.

The two factors determining the truth of that statement are:

• If you are competing in a highly competitive market.
  For instance, the number of hits on a site can influence the ranking. Some companies pay out huge sums advertising their site in other mediums. These campaigns ensure a high hit ratio.
• Partnership deals are struck that involve site positioning.

It is important to focus the site at SE's that draw traffic for a particular keyword. That should be the first priority, however mergers and take-over can suddenly change the fortune of a Search Engine. AOL for instance draws its search results form Google's database.