Unlike those internal polls, the mainstream polls have an agenda, which is to sway the populace to a desired outcome. I do not think any reasonable person could argue that the mainstream media has a liberal bias and would like to see the Democratic ticket win in any presidential campaign.
Therefore, the mainstream polling will reflect that. Methodologies will be adjusted to achieve the desired outcome. If registered voters need to be chosen over likely voters to better reflect the desired outcome, it will happen. If Democrats need to be oversampled to achieve the desired outcome, so be it.
In this manner, the MSM hopes to "shift" most of the undecided in their favor. They understand that many of the undecided want to "vote for the winner" so they make sure that their guy is seen as a winner so that they can hopefully make their wish a self-fulfilling prophecy.
Now these polling companies do need to have some credibility so that they can be taken seriously in the next election cycle. So in the days leading up to Election Day, you always see a "surge" with the GOP candidate. But that surge is manufactured. It is simply a function of the MSM polls adjusting their methodologies to reflect the true state of the race. As I said before, the MSM is hoping that they shifted enough votes over to their side with the earlier skewed polls to make the difference.
So when the mainstream media see conservatives getting angry over the polls, they are literally squealing with delight. For not only are they shifting votes their way but they are angering conservatives so much that many of them might just throw in the towel and stay home on Election Day, thinking that their cause is lost.
On the other hand, the "internal" polling is reflecting the true state of the race. It is vital for a candidate to have accurate polls because those polls will determine where they spend their limited resources and where they spend those resources will make all the difference whether they can win or not.
So I have always stated that if you want to know what a candidate's internal polls are saying, look at where the candidate is campaigning. Recently, McCain and Palin have been campaigning in places like Minnesota and Wisconsin where the MSM have already determined that Obama has it wrapped up.
In conclusion, hasn't anybody ever wondered why a national presidential campaign would need to spend money on "internal" polling? It is because they know that the MSM polls are not accurate. Otherwise, they wouldn't need internal polling at all because the MSM is hitting us with polling data every single day. The only problem is, none of it is accurate so the candidates need to do their own polling to see where things really stand.