The Falcons went to Worrilow because Stephen Nicholas is no longer an effective starting linebacker. Even his strength, stopping the run, hasn't been a true strength in 2013. Worrilow is the better athlete now, he's better in coverage and the Falcons are able to limit his exposure because they play a lot of nickel. That was before the injuries, of course.
Trueblood was pressed into starting duty because he's simply the better run blocker and right tackle than Lamar Holmes, which isn't saying all that much. The Falcons are woefully weak along the offensive line, so Trueblood qualified as a legitimate upgrade. To his credit, he's played fairly well, and we'll just hope he continues to do so.
With Sam Baker hurt, Lamar Holmes may still have a spot in the starting lineup for the next couple of weeks regardless. Injuries to Akeem Dent and Paul Worrilow mean that that depth chart might also be meaningless this week. This has been a brutal year for injuries.