Re: prime minister or prime marionette
as others have pointed out, you are completely incorrect in your contention that the majority political party is the head of state in a parliamentary system or that political parties make all the decisions in a parliamentary system. The ONLY dependency the executive has on the legislature is through a vote of confidence/no confidence measure, otherwise it is very common, infact the norm, for the prime minister to have tolerably large divergence with party positions.
For reference please see the actions of Tony Blair vs the politics of Labour, and his unpopularity within the party. Please dont tell me UK isnt a parliamentary democracy. That is one example, please dont spend time fixating on tony blair's personal circumstances or that he is caucasian, please feel free to cite any other stable, well developed parliament where the prime minister keeps running to the party for every decision.
Now finally you say what is the difference between zardari and PPP? none. sadly PPP is a one man party, much like other political parties in Pakistan. However that one man party merely accentuates the extent to which Gilani's "what should i do now father" is unseemly for the Prime Minister of a country of any worth.