I see your point. But the popular vote almost always predicts the winner of the Electoral College. There are exceptions such as in 2000 with Bush/Gore but that was a very tight race with Gore getting 48.4% to Bush's 47.9%. I think you have to go back to 1824 for another example and that was a very close race too.
There is no example of a candidate being well ahead in the popular vote and not also winning the electoral college vote. That's probably why we see so many national polls.
This nation is divided, and from 2008 & 2012 we see how difficult it is now for any Republican to win. Unfettered immigration and the welfare state w/ more than half in the wagon & less than half pulling it make victory for the GOP a crapshoot. We’re going to see more close Gore v. Bush or not-so-close Obama v. McCain/Romney going forward. And that will make national polls less predictive, IMO.