Speaking to media outside the High Court at Christchurch after Weatherston was sentenced by Justice Potter, Mr Elliott also said: "Life ought to mean life, of course, like it is in America, but unfortunately it's not in New Zealand.
"So I guess 18 years is probably reasonable under the circumstances.
"We would have liked more, but at least it's not manifestly excessive and therefore probably won't be appealed."
Weatherston, a former Otago University research fellow, was found guilty in July of murdering his former girlfriend, Miss Elliott (22), by stabbing her 216 times at her Ravensbourne, Dunedin, home on January 9, 2008.
During the sentencing, Weatherston's lawyer, Judith Ablett-Kerr, said Weatherston had asked her to tell the court he was sorry.
Commenting on this, Mr Elliott said he considered Weatherston's apparent show of remorse "nonsense".
"That guy has never shown any remorse. He never pleaded guilty and he's never said sorry, so no, we don't believe that."
Miss Elliott's mother, Lesley, said the family was pleased with the judge's comments and thoroughness.
She also rejected Weatherston's continuing claim that his daughter provoked him by attacking him with a pair of scissors.
The Weatherston family and their lawyers left the court building through a side entrance without making any comment.
Miss Elliott's cousin, Linda Curtis, said the sentence was a "bit of a let-down", but it was always going to be, because it would never bring Sophie back.
She knew Mrs Elliott had hoped for a sentence of more than 20 years. However, she thought the judge had done a thorough job within the existing laws, Ms Curtis said.
The family had been so relieved after the guilty verdict and so focused on that, they were exhausted now, she said.
Miss Elliott's family members, one after the other, told the court yesterday how Weatherston had not only taken their daughter and sister's life, but their lives as well.
"Clayton, you are the epitome of evil," Gil Elliott said as he delivered his victim-impact statement during the sentencing.
"Everything I had existed for stopped that day. Sophie was the light of our lives. She was a gift from God; we all thought so."
About 80 people, including the Elliott and Weatherston families, supporters and police, sat in the public gallery yesterday.
In her victim-impact statement, Mrs Elliott talked of the day of her daughter's death and seeing her daughter being stabbed even after she was dead.
"My beautiful daughter had been butchered. I saw her body lying there covered in blood; the body that only minutes before had been warm and given me a hug. I will never forget the terror."
She now cried herself to sleep every night, took medication to keep her functioning on a daily basis, had taken all her available leave, and more, and reduced her hours of work.
"Clayton Weatherston, this is what you have done to us... I hope her screams of agony ring in your ears as they do in mine."
The Elliotts' other children, Christopher and Nicholas, also said in impact statements they had been affected profoundly by their sister's death.
Weatherston's father, Roger, his voice cracking with emotion, spoke of what a normal boy his son had been. "I hope Clayton can find it in himself to publicly show remorse."
Weatherston's lawyer, Judith Ablett-Kerr QC, later told the court Weatherston had asked her to tell the court he was sorry.
"He tells me he is sorry, that he saw no point in saying it himself because it would appear contrived."
But his apparent lack of remorse contributed to Weatherston's sentence. Sentencing Weatherston to a minimum non-parole period of 19 years, Justice Potter deducted a year for his lack of previous convictions and that he was likely to respond well to therapy for his various conditions, including obsessive compulsive and narcissistic traits.
Prosecutors had sought a minimum non-parole period of 19 years for the murder, while the defence recommended 12 years.
Justice Potter said a pre-sentencing report had described Weatherston as being full of remorse for what happened, but it was mainly for his own situation.
She described the murder as deliberate and controlled, and rejected the defence that Weatherston was provoked.
The continued attack and mutilation of Miss Elliott's body after her death left her in no doubt this murder was committed with a high level of brutality and callousness and was among the worst murders, Justice Potter said.
Her decision was greeted with silence in court, Weatherston showing no visible reaction.
Outside the courtroom, reaction to the decision was also muted.
