Systematic vote machine fraud, "Default to Bush" has been documented in swing states such as Ohio, Florida, and New Mexico- and some of this has been observed in other states as well.
http://www.flcv.com/fraudpat.htmlhttp://web/northnet.org/minstrel/youngstown.htmOther types of systematic fraud have also been observed in many areas.
These appear to explain the swing to Republican seen by the difference in the exit polls and official vote totals.
This means that Bush or another default candidate would get not only the votes of those who didn't notice that the intended candidate didn't register, but any intentional non votes or accidental non votes or unsuccessfully completed votes. Quite an advantage. Under normal circumstances this would result in a swing as much as 2 to 4% in many areas. But since it is a matter of record that the default was hard to override and sometimes impossible as reported by the EIRS reports and acknowleged by poll workers, only the most watchful or purposeful voters may have been able to successfully vote for a chosen non-Republican candidate. Thus the swing was likely much larger for some machines and even more in some minority precincts that appear to have been targeted to produce high levels of misvotes based on the large number of EIRS reports in minority precincts. There were also a few cases where precincts had machines set to default for a minor party candidate, but none observed to default to Kerry. These patterns have been confirmed by analysts and computer experts in several counties of each of these states. Other similar default related patterns have also been observed in some of these areas, such as failure to register a presidential vote when a voter tried to vote straight party line. This would result in the presidential vote going to the other “unintended” party.