Except psykers that can't be part of units, or are not commonly actually put in units, which there are plenty of actually. And a bunch of them are monstrous critters that you wouldn't have much of a chance to wound with a boltgun besides. Ever played against Tyranids? How about Chaos Daemons?
Besides, you actually have a better chance to hit a psyker in a unit with this one in the new edition, unless they are in the dead center of a swarm of models and then - it will be the same as last edition.
Well actually it is impossible to "hit" the psyker in a unit. You can hit the unit, but you can only allocate wounds to the psyker, and most of those would be a character at least so the opponent could LOS the wound away.
A one-shot S5 AP- isn't really going to be worthwhile shooting at Flying Monstrous Creatures, even if it causes a Perils of the Warp on an unsaved wound.
Wife: "How much do you have invested in these ... miniatures?"
Me: "I don't think invested is the right word."