I'd say it has less to do with fear of typecasting than it does with being bored. He's been playing an iconic character for six years now, so its too late to worry about typecasting for the most part. He's probably in a better position than most though because any future roles will likely involve hair. :)
He's had a great run as Lex, but eventually TV stars get bored or feel they can't bring any more to the character. They don't necessarily get bored with the paychecks, hence some shows/characters overstay their welcomes. But its not unusual to say enough is enough.
Smallville itself is also on its last legs, and its future depends on how long the writer's strike lasts. The CW is rumored to have all of its scripted shows on the chopping block right now, and the networks are using the strike to take stock of their programming budgets and kill off any shows that under-perform in ratings/advertising compared to their budget. Smallville gets decent ratings with a key demographic but is also the most expensive show on the CW. If the WGA strike continues through summer/fall (expected) and SAG joins them in June (expected) then I wouldn't be surprised if there isn't a house-cleaning at the CW. Smallville has a rabid fan-base, however, so I would expect them to either finish out the current season (completely retooled, and probably not til 09) or give it a big send-off two-night special or something.
FYI, there's no tie-in between Smallville and the Justice League feature film other than they are both DC/Warner Bros properties. Justice League was already in the casting process when the strike happened (delayed because they don't have a workable screenplay) and they are going with no names in the cast and skewing much younger with their actors (Rosenbaum is in his mid/late 30s now). The storyline is expected to be a "reboot" of the comic book and exist in its own "universe" - there's no tie-in to the Christian Bale Batman movies either. Superman is a major character in JLA, but he won't be played by Tom Welling (or Brandon Routh). Warner Bros is more likely going to try to use JLA to springboard Wonder Woman and Flash feature films rather than tie back to their other DC franchises.
If any of this is even remotely interesting or helpful...
Anywho, the guy in the pic has a hot bod and cock :). | 
