[tusaki]

The theory is that in a 2 party system, both of the parties will adjust their policies so to attract as many voters as possible. Let's say you put all of the issues on a left/right graph. There is a golden middle. 1 party sits a little on the left of the golden middle, the other a little on the right. This way, both attract as many voters as possible. The idea is that no matter who wins, the ideas of the majority are always somewhat supported. This could explain the 50/50 elections.

http://en.wikipedia.org/wiki/Two-party_system

The two-party system's defenders argue that it produces more stable governance than multiparty systems, because coalition is highly unlikely to occur with two parties dominating. it keeps 'undesirable' extremist parties out of power, like the British National Party (which most Brits perceive to be racist) in the United Kingdom. uncommon, unconventional ideas and ideologies are non-influential, so policies and governments do not change rapidly; though there is some controversy as to whether this is an advantage. While smaller parties find this exceptionally frustrating, proponents suggest that it enhances stability while allowing for ideas that gain favor to become politically influential. it gives a more transparent choice to voters: coalitions are created internally before the election rather than externally after it; it is easier to judge whether an elected government has delivered its promises since it cannot blame component parties' diversity for failure. the dynamics of a two party system drives both parties' policies towards the position of a mythical median voter while remaining distinctive enough to motivate their core support. and even that two party systems, especially those where power often changes hands, are less prone to revolutions, coups, or civil wars. Against the argument that the two-party system leads to more stable governance, critics of the two-party system argue variously that: stability is not desirable in itself. the two-party system produces stable governments, rather than stable democracy, and the latter is what should be desired. two-party systems are not intrinsically any more stable, citing such examples of stable democracies as Germany, which has a multi-party system through proportional representation. The two-party system is also criticised for the following flaws: Candidates are motivated to run negative campaigns, pointing out the flaws in the "other person" (usually the leader of the other party) and staking out only those positions that are necessary to differentiate themselves from their primary opponent and not constructive or beneficial to citizens. If the opposition party is weak, a dominant-party system may develop. Debate in the assembly of the country can often be adversarial and not constructive, sometimes revolving around narrowly perceived policy ideas, rather than larger political issues. Sometimes adversarial politics can lead to the opposition disagreeing with everything the government proposes (and vice versa) for the sake of disagreeing. This can lead to important legislation, especially reforms, being blocked that may be beneficial for the country. The system is more easily corrupted by campaign contributions since there are fewer players to donate to. In an effort to attract voters, each party will adopt planks of the other party's platform, leading to the appearance in some skeptics' minds of a one-party system. Examples include the American notion of a "Republicrat." The electoral systems which tend to favour two-party systems (notably the "biggest pile of votes wins" system) are also criticised because: Most electors are forced to engage in tactical voting, voting for candidates that may not be their first choice. Smaller parties will be unrepresented: they will not receive a number of seats in the country's assembly that reflect the number of votes received for them (and therefore the amount of support for them). Some argue that this is undemocratic, as citizens who vote for small parties should be represented fairly. Smaller parties often represent unconventional or 'alternative' (compared to the main parties) ideologies and formulate policy on the basis of this ideology. It can be argued that in a democracy, all ideologies should be fairly represented. Larger parties will benefit from being overrepresented; some argue this is undemocratic.