Well the bolt thrower on the stegadon's back certainly shares a lot in common with a warmachine. But GW has once again stuck with a separate...
I am totally in agreement with Daeghrefn here... this weapon is able to do things that will force the enemy to either severely alter his battle...
To carry on with the dwarf comparison, the only reason you can use the engineer's BS is because he has a special rule called "Artillery...