That's only if you go by yards allowed. Football Outsiders has them down as the 15th best pass defense, or "undeniably average", and that's closer to the truth. The yards allowed is so low because the rush defense is SO BAD that teams don't need to resort to putting the ball in the air to pick up first downs against the Chargers.
2. How concerning is it for the Chargers to be without Eric Weddle and Manti Te'o? What do you expect from their replacements?
Manti missed last week's game and his replacement, rookie Denzel Perryman, forced a fumble and spent most of the game terrifying everyone on the field with his big hits and brilliant play. That spot might actually be better without Manti.
Weddle is, probably, the best defensive player on the Chargers. He hasn't missed a game in a very long time. His presence will be sorely missed, and could cause major issues in the deep pass coverage for the Chargers.
3. We know about the Philip Rivers to Keenan Allen connection. Have they been carrying the torch or are there other areas that have been especially strong for the Chargers this season?
Well, since his return from PED suspension, Antonio Gates has been like a young Antonio Gates. That has helped free up Keenan Allen, who was already having a pretty good season, even more. Mostly, though, this offense has been about Philip Rivers playing some of the best football of his career irregardless of who else is out there on the field with him.
4. I really expected big things from Melvin Gordon right away. Has he shown any flashes that he can be great or just a disappointment? How have the Chargers gone about trying to replace the production they expected from him?
The answer to the first part of your question is that there have been a couple of flashes that show off his tremendous athleticism and strength, but his hesitation behind the line has killed him, and his fumbles (4 in 6 games) will probably land him on the bench this week.
Before this week, the Chargers have tried to force Gordon to succeed, trying to get him the ball every which way in hopes of getting a big play from him. So far, it's done nothing but stall the offense. The times when the Chargers move easily down the field and into the end zone have coincided with Gordon being on the sideline. Expect a more consistent performance this week on the legs/back of Danny Woodhead and Branden Oliver.
5. This may be a broad question, but how is it Philip Rivers can be on a record-setting pace and yet the Chargers are sitting at 2-4?
It's a two part answer.
First, Philip Rivers is really good. He's the modern-day Dan Marino. There aren't many passes he can't make, I don't think I've ever seen a QB with better touch on his passes, and he's exceedingly intelligent.
Second, those stats (Rivers is on pace to break single-season records for passing yards, passing attempts, and completions) are the result of the rest of the team being terrible. There's no running game to lean on, the defense gives up a ton of points and can't stay on the field very long, and so Rivers gets a lot of opportunities to throw the ball.
Stats like passing yards, passing attempts, and completions don't win games. In fact, most QBs put up their best numbers in these categories when their team is losing. So, that's what Philip Rivers is doing. Putting up some of the best stats of his career on one of the worst teams that he's been on.
I will link to my answers to his questions when they are posted.