I completely agree that for OP's goals, 10-12 repetition dead-lifts will not help him get anywhere.
However, the repetitions one does are based on what they are trying to achieve.
Some broad examples are:
Strength:4-6 reps/set
Size: 7-10 reps/set
Endurance/fat burning/cardiovascular focused: 10-15 reps./set
I *never* recommend anyone to do more than 15 reps, and often not even more than 12 reps per set. If someone can do 20 reps in a set, then they clearly need to increase the weight.
All the people who are recommending 20 reps simply do not know what they are talking about. Those same people will also try to make up some B.S. as to why something else I said is not correct, just to make themselves not look dumb. However, to people who know what they are talking about, those people only make themselves look more foolish. It makes no sense to come on here to act like you know something when you don't - unless of course you don't have a job, are not looking for one, and have nothing else better to do with your time.
In short, do *not* do 20 reps, *especially* if you are looking to get results and gain size and strength to any extent.