It's the people that create it. It is not technically difficult to tabulate millions of responses accurately so long as it remains an exercise in simply counting things. The complicating factor is that the results serve to distribute vast amounts of money and power which creates motivation for fraud that undermines that simple process. We should have no illusions about the accuracy of the tabulation process until there is open source code, paper audit logs and the opportunity for the public to examine these records for signs of fraud. Perhaps as an additional safeguard statistical comparison with exit polls should be required by law and any significant deviation should trigger an investigation of the process for possible tampering. These technical issues are only symptoms of the real problem.
"Proverbs for Paranoids #3: If they can get you asking the wrong questions, they don't have to worry about the answers." -- Thomas Pynchon