As your raid leader, there is no reason I'd put anyone else but you as DPS, because you're the highest. Period.
If there's anyone to blame, it's the other healers that fail at DPS, not the leader. He's just doing what is best for the progression of the raid.
Finally, your case is very weird :P. In my guild, me and the other healers fight over the DPS spot on the 2-heal fights (we 3-heal the first two, for some reason) ALL the time. I end up getting it 90% of the time though because I got lucky and got both of my 489 weapons for enhance on the first week ^_^.