The rock singer, who was eliminated from the ITV1 reality series yesterday, had been accused of being a diva by the press and was criticised by Webber last night for "nonsense" tweets and arrogance.
Fans of James, who was topping Digital Spy's poll for who should win the show, claimed that Webber's comments were inappropriate.
One reader said: "I was outraged that a man of ALW's standing was so unprofessional I have no respect for him at all now, he did not critique Nathan James's vocal performance because quite frankly Nathan's vocal ability is phenomenal!
"Instead ALW spewed forth a malicious tirade of Nathan's Twittering! Castigating him for retweeting a hand drawn picture that a fan had done! But David Hunter retweets real pictures his fans have mocked up clearly depicting him as Jesus!
"Nathan James bowed out of the show with grace and dignity, something that ALW needs to learn! I think the biggest ego of the evening was the very childish unprofessional ALW ! The bunch that are left i wouldn't pay to see."
Another James supporter wrote: "That was disgusting, ALW's horrible personal vendetta against Nathan was completely unprofessional - it's a vocal performance competition, who gives a monkeys what he's tweeting.
"Nathan was by far the best of the final 5, definitely better than Roger - who's voice cracks all over the place. Very disappointing."
Copyright: ITVJanet Pyer said: "I find it hard to believe that the best singer in Superstar has been voted off. I am simply not interested in the remaining four."
Meanwhile, Sara Cooper commented: "The moment that Nathan was eliminated I turned the television channel over. I wouldn't give the the others the time of day, let alone pay to see the show."
However, Webber's comments were defended by some fans, who described James's behaviour on Twitter as that of a "big headed idiot".
Anna Masera Crumpton said: "I have to say, there is a fine line between confidence and arrogance and Nathan definitely crossed it.
"I admired his singing, he is mega talented, and he has fantastic stage presence, and he can act. But, I just did not feel comfortable looking at him as Jesus. He smelled of over confidence, Jesus was humble."
Superstar continues tonight (July 24) at 9pm on ITV1.