Each generations have their Justins. Elvis was not popular amongst parents due to his vulgar dancing as seen in those days. Probably Beatles were considered bad influence at that time. So I think it is OK to have a Justin amongst us. But respecting individual choices and not taking anything away from young generation freedom of choice, at least J. Bieber should have practiced to perfect lip sync and give Indian audience their moneys worth. Which was not so in this case as I read. But also nowadays it is about making more money and for this particular show the managers, artist, music companies must be happy. Artist was in and out of India in a day and the team made millions. Look around us, these days stars are created by hype and media. Cricket Legends, Movie Stars, Singers. It is all about making money. Not complaining though, everyone has a right to make money.
Another reason for lip syncing is may be most artist these days use Autotune. Music companies regularly use Autotunes, Echo etc. repeating lyrics ("baby, baby') which makes almost any song a success. Giving live performance without 'Riyaz' may give away their voice's negative side. To have a real live concert is probably more difficult than recording. It needs hours of practice to refine the voice. Lots of physical hard work, setting audio system etc. Probably the greatest critically acclaimed live show was by Queen at Wembley Stadium.
Here is my favourite singer live. With bad recording and at this age she still sings beautifully. That is because of practice, dedication and sticking to classical form. You be the judge.
https://www.youtube.com/watch?v=x5H0-Vt_S_U
A very popular anecdote is that M. Rafisaab refused Royalty (extra money) from his singing saying that he already gets his money for singing a song so why should he ask for more. Class vs Mass.
Regards.