Polls aren't hard to figure out.

Why is it so many can't understand why the polls continually-despite the shortly lived bounce-show Sen. John McCain and Sen. Barack Obama essentially in a dead heat? Obama isn't running against President Bush, he's running against John McCain who has had 20+ years to create his own "brand". McCain is also still seen as a moderate Republican despite his consistent pandering to the GOP base.
Consistently polls (some saying 65%, some saying as high as 80%) are coming out saying that the majority of Americans don't support this Iraq war or are tired of it. My bet would be that not all of those people want an immediate, timetable, non-conditioned based withdrawal; this of course isn't what Sen. Obama has been saying his plan is but the McCain campaign has successfully created the belief that it is. This is supported by the polls showing that the majority of American's feeling more comfortable with Sen. McCain's plans for Iraq and his handling of the situation in general. As I've mentioned before, Obama would allow conditions to "adjust" his tactics for withdrawal but he doesn't emphasize that enough, he doesn't emphasize it strongly unless pressed to do so. This is mainly because it would run the risk of disenfranchising those who feel they're voting for him as a vote against the Iraq war. This shows Obama's nuanced stance in more specifics-mainly from Obama's own words: http://marcambinder.theatlantic.com/archives/2008/07/on_iraq_an_important_semantic.php

The more important and bigger truth is that this country has a great divide as to how we move this country forward. No matter how bad this economy gets or how Afghanistan moves along, good or bad, or how well Iraq has been doing, most people have made up their minds as to where they want this country to go and who they want to support. It isn't likely that more than 20-25% of voters don't already know who they like or at the very least, which political party they tend to relate to. The cliche would be only 20-25% are "in play". This country also has two candidates with huge differences policy wise which for a lot of voters, especially those that only vote based on one or two issues, makes it a lot easier to make up their minds.
A lot of older Democrats-some say Reagan Democrats if one wants a label-feel that the party is leaving or has left them. A frequent mistake though is that a lot feel this is seen only on social issues but in reality it also has to do with energy policy, perceived over obsession with saving the environment, and yes, even expansion of the Federal and State governments. Their are a great deal of people that feel they're a Democrat socially but more Republican economically and when the economy is in the toilet, that, despite the Republicans being in power for 8-16 years (depending on how one sees the Congress), still probably helps McCain. Especially when his campaign makes the case that Obama will raise everyones taxes despite the fact that if you make under 250,000 your taxes will go down or stay the same. You also have quite a few polls saying that 60-70% of this country supports/wants more drilling, Sen. Obama doesn't support that. That puts a cap as to how far ahead he can pull away, especially and specifically in the mid-west and non-coastal states who support off-shore drilling by larger margins than coastal states.

In the end the polls will continue to stay close with bounces here or there but this is about Sen. McCain's brand vs. Sen. Obama's newness, it isn't a matter of the Republican brand vs the Democrat brand. That's even though both are very much representatives of their respective parties staunch beliefs and policies.

Edited: 7/26