In WordPress you will see a list of all posts and pages on the site if you omit to add a search string and then click the submit button. The only reason that I can think of why WordPress does things this way is because the search functions are also used in the admin pages e.g. on All Pages and All Posts. On both these pages there are filters that include ‘All Categories’ and ‘All Dates’. For both these filters the search string will be empty but still WordPress has to return all the entries.
Many longer WordPress blog posts are split up into multi-pages. The thinking is that the page loading time will improve, the bounce rate might decrease because the user might stick around a bit longer and the marketing guys say it is a way of adding more ads. Whatever your reason the feature is pretty nifty and easy to use.