Genomes, Genes, And Gene Therapy

There was an article in the Sunday paper about Ozzy Osborne having his genome sequenced. 

Last night there was the first in a new drama series about a man who finds out after his wife's death that he may not be the father of all of their children - and he is given a DNA kit so he can find out.

Then on the TV tonight there was a programme about gene therapy and how the future is shaping up.

It seems to be gene-talking time.

And I am thinking that with billions of items in the genome sequence it seems remarkable that there are not more mutations in the pairing and copying process as each new person is made.

I recall someone I knew a long time ago (he had a mouse named after him) mentioning that mice have a high rate of mutation in their offspring. Why, and why don't humans?

What is the answer -  redundant circuits - longer gestation for faults to kill off the mutant? Something else?