This question is a variation of one of the oldest accusation that every cop hears at some point in their career:
"Don't you have anything better to do?"
The fallacy here is that whatever the problem the citizen in question has found themselves in, somehow, somewhere, there is a more important statute being violated by some other individual that should be enforced before the citizen in question gets cited/arrested/whatever for.
There's a related version that CHP officers get to hear on a fairly regular basis, the driver that's been stopped who points out passing drivers who (in the stopped driver's pov) are speeding and demands to know why the CHP officer isn't stopping them instead of...
Yeah, it's infantile and never results in a diversion of attention on the part of the LEO away from the violation at hand, but it is what it is.
WRT Assange, it's my understanding that sexual assault is taken seriously in Sweden, and other than his prominence, this isn't an unusual prosecution.
WRT prosecuting Bush, first they'd need to have jurisdiction. To the best of my knowledge, Bush isn't accused of violating Swedish law on Swedish soil, so that first hurdle might not be overcome.