Search engines were never created equal and as they have grown up they have taken slightly different paths. Consequently, identical search terms entered into a different search engines will return different results. If different search engines return different results then it stands to reason that different techniques may be required for each of the search engines.
You could try to undertake optimizing your website for all of the major search engines, and most sites do. Many sites concentrate their search engine optimization efforts on Google and hope it is enough to satisfy the other search engines. However, with a little research you may be able to concentrate your efforts on the search engines that will deliver the most traffic and sales. Demographics of your audience is one set of statistics that could be very important to your decision making processes.
Finding statistics on demographics for search engines takes a little research. However, the following statistics, although approximate, may give you an idea of current trends.
18-34 year olds prefer to use Yahoo!
Over 55′s prefer to use MSN
Males tend to prefer Google
Females prefer either Yahoo! or MSN
Google searchers are more likely to buy compared to Yahoo! and MSN
If your target audience group is female and between the ages of 18-34 then targeting your SEO towards Yahoo! may be more effective in the long run. If your target group is female and over 55 then perhaps MSN may be more productive.
Statistics never tell a complete picture and since Google receive over 70% of all search traffic, it would be foolish to ignore their search engines. However, knowing where your potential customers are likely to come from can help to refine the SEO for your website.