I think there's more to Hilfenhaus just not taking that many wickets than just being "unlucky" though, really. He's a good bowler, but his bowling style and his minor flaws make him look better than he is. He swings it straight from the hand which looks good on TV and in the stands but is a lot easier to play as a batsman than someone who swings it late like an Aamer for example, and he doesn't attack the stumps which gives the batsman freedom to leave a lot of him (and unlike with Johnson, they tend to). Furthermore, he only moves the ball one way which makes him less effective to right handers than he'd otherwise be - against left handers, the one that angles across with that off-cut action is a very useful variation, but he's been unable to set right handers up for it because it just doesn't move enough or have enough angle on it to really cause a problem.
With the swing he gets, his natural length is just a fraction short to take the edge, and if he pitches it up further the batsmen can line him up because it swings so early.
As I said, he's a good bowler and I'd have him in the team, but I think these factors make him less effective than he first appears.