It's not really surprising to be lacking hard removals or silences on turn 4, which is the earliest that combo can be played. And that's 10 damage ON turn 4, with potential loss from that combo alone on turn 6.
Plus, the Imp Master isn't an attractive trading option. It'll take multiple minions to trade for it at that mana point, and it spawns a 1/1, which won't take multiple minions. So that already gives the Priest a fair bit of insurance that they'll be seeing at least 10 damage from it.
Now, obviously, it has weaknesses with the fact that any damage on turn 3 diminishes it's return on 4-7. But still, it's such an unattractive target if the Priest is playing well, that's not a huge issue.
And Priests have really strong early game control, through SW:P, and cards like Northshire Abbey are going to be natural minion draws, which will protect the Imp master.
Plus, any hard removal used here is one you can't use down the road, so it still gives a nice advantage to the Priest. They used two meh cards and one solid card to trade for one of your BEST cards. That's not a bad deal at all, particularly when they also got 10 damage in the trade.
It's also worth noting that your removal will probably take all your mana at turn 4/5, so that keeps you from doing any other board maintenance.
Anyways, you all are horrible, @#%^ed up people
Never underestimate the healing power of a massive dong.