How Happy Should I Be?

The Washington Redskins just completed a perfect 4-0 preseason. And our starting QB Robert Griffin III didn't take a single snap.
I really want to believe that this shows something special about the defense, or the offensive line and that once RG3 comes back (if he's at full health, a big if) the Redskins would have to be even better.
But then I looked at this list of NFL teams that went undefeated in the preseason.
Last year the Seahawks went 4-0 and it portended a strong season. But the Eagles also went 4-0, and then went 4-12 during the regular season.
Remember the year the Lions went 0-16? They were 4-0 in the preseason that year.
From 2000 - 2012 inclusive, 25 teams went undefeated in exhibition games. 13 of those teams made the playoffs (52%), 2 of those teams won the Super Bowl (8%), both of which are better than the random expectations (37.5%, 3.3%) but hardly a guarantee.
Now I know that this last game against the ExpensiveCornPrices was played entirely by Pat White, a QB who won't even make the team (though he could be first string on the Jets), but the defense only gave up 6 points in 4 quarters, and played similarly well in the other three games.
If the defense is improved and RG3 is healthy, and the team made the playoffs last year, why is another 10-6 season out of the question?
Or am I getting ahead of myself?