I've checked some steel wheels myself with a gauge and they are 114.3mm/4.5" EXACTLY. They never used the Merc 115mm pattern.
And the pattern hasn't changed. I just check RockAuto for a 2013 Challenger SRT8 front hub and it fits Challengers from 2008-2013, 300's from 2005-2013, Chargers from 2006-2013 and Magnums from 2005-2008. The same hub for all of them. I didn't verify, but that should include the full range of production of the LX/LC cars. So unless they have multiple patterns machined in the hub (and they don't) the pattern has stayed the same from teh beginning.