We're talking plugs, not plug wires, right?
The plug wires require either the special MB tool (or a pair of pliers, in a pinch) for removal. Otherwise you can break the holder(s).
And yeah, over a several-thousand mile period, the differing alloys of the spark plug and cylinder head coupled with heat creates a chemical reaction that essentially "welds" the plugs to the head...hence the herculean effort required to remove them!
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car