I guess that's what's funny about baseball. Even your best teams are going to have a hard time sweeping a four game set vs. an opponent but that loss still counts heavily. Personally, I think RPI is over-rated because like the strength of schedule argument in football; the only way to truly help your SOS is to lose.
I mean if your opponents have a record of somewhere around 475 wins and 525 losses but your team record is 40-11, then looks can be deceiving. That means that your opponents, when they don't play you, were actually 486-485. That may not sound like much, but looks a heck of a lot more impressive. (The numbers work better in a football argument just because of a smaller sample-size of games but the same principle applies)
There's a reason this team is towards the top of most of the human polls. RPI doesn't take the human element into consideration. (the human element of the players, not the voters) Texas dropped two of three to New Mexico to start the season, but I don't think anyone in their right mind would put the Lobos ahead of the Longhorns on their ballot.
My take on this TCU team so far is that they do get into a habit of playing down to their opponent in some instances. But what it really boils down to is the fact that if the weekend starters were also starting the weekday games, I think we'd be talking about a team with a record of about 45-6.