You are correct, and I am not just saying that because you are a Redskins fan either.
Any season that allows the team to have a shot at the postseason should be considered a success. The problem is that the expectations are a bit higher here for a team who has secured the #1 seed 2 years in a row, lost the past 2 SB's in the final moments of the game twice in 4 calendar yrs, have arguably the best QB and HC combo in the history of the game, and made several bold moves to equate to better defensive results.
If the defense (more correctly the secondary) didn't look so shaky at times, then more fans would feel "comfortable."
The worry is that we will once again have a 12-4 or 11-5 record only to falter in the postseason due to repeating the same old mistakes over and over again, which may not be entirely true or entirely false either...but that is pretty much the worry and frustration.
Now if you go back to the days where they missed the playoffs every year on a consistent basis, then you'd be in the same company as current Redskin fans who just want to taste the postseason again.
Should the 'Skins have the best record in the NFL over the next 10 years and secure 2 #1 seeds in a row to go along with 2 last minute SB losses, then you'd be in the exact same scenario, as your fans would "just want that one more elusive trophy" too.
The biggest regret and sense of frustration is that they are so close, yet have to bear witness to watching the same mistakes from the secondary/pass defense, despite many wasted high picks and free agent moves etc.