The unemployment rate often goes up and down every month, every year etc. When you look at a persons time on the job, its important to look at every month, not just the first month and the last month. Even in your hypothetical examples, or Presidents Bush and Obama, its not accurate to say that only the first month and last month, TWO MONTHS, of data are the only relevant data out of a total of 96 months.
IF, you only looked at two months of data, you would miss the fact that for most of George Bush's 8 years in office, the unemployment rate was relatively low.
Its important to look at all the information/data and average monthly unemployment data is an important figure to look at. George W. Bush's relatively low average monthly unemployment rate was a contributing factor to his re-election as President in November 2004.
The problem with certain types of cherry picking of particular data, only certain months, or this or that economic statistic, is that you miss a lot of other things. To overly focus on George W. Bush's last months in office in attempt to cast him as the worst of the worst, you miss out on things like the fact that George W. Bush was actually re-elected President and the reasons behind that.
Its sort of like Oliver Stones little movie about Bush called W. Oliver Stone does everything he can to ridicule Bush in the movie, throw the kitchen sink at him, but fails to mention that when the American People at large had the first and only chance to say what they thought about the work he had done, they re-elected him. George W. Bush's re-election does not fit the narrative of Stones film, so it's not included.
