*bump*
Sorry, I know this thread hasn't been posted in for a year now, but I came across it & just had to counter this.
In political science, the tendency being referred to above, in which plurality-rule elections (such as FPTP) structured within single-member districts tends to favor a two-party system, is called Duverger's law.
Duverger actually didn't regard the principle as absolute, suggesting instead that plurality would act to delay the emergence of new political forces & would accelerate the elimination of weakening ones, whereas proportional representation would have the opposite effect.
Since 1987, the Philippines is seen as basically the only country whose politics run counter to Duverger's law, as the Philippines' governance structure changed repeatedly before 1987 & the country has many distinct social groups.
So... yes. FPTP does naturally levitate toward a two party system.