They have occasionally done 2 part episodes, so this is not terribly unusual; however, they've kept this to a minimum because of the complications it causes when syndicating the series. Series such as Lost or 24 are not practical for general syndication, and viewers really need at least a summary background before viewing newer episodes. Even 24, in which an entire scenario/plotline is complete within 24 or less weeks, really needs some background on Jack, etc for a new viewer.
Just catch our "friends" at TNT when they run several episodes or a mini-marathon of Law & Order, with the possibility that one episode could be 15+ years older than another. In early shows, cell phones were not yet popular, so the cops are using pay phones. I think that Benjamin Bratt was the first to use a cell phone.
And...it really gets complicated when episodes "cross series": There is an episode of L & O that is completed in an episode of "Homicide: Life on the Street." That one episode of "Homicide" is distributed with L&O to allow that plot line to be completed. And...vice versa.