No offense taken. Just a few points -->
one: as you already pointed out, many times singers are taken based on their availability. I do realize that Udit has really cutback on his singing assignments, maybe as he realizes that people expect 'newer' or 'hip' voices, or to make way for his son. two: As much as I just adore Rahman, I would just take one step back and not be under the illusion that anyone's perfect. Rahman's music has been a big part of my life, and I do respect him and worship him -- I do also understand that there are times when the songs are not the absolute masterpieces, albiet very very few. three: it was just my humble opinion that Udit might have been better for the song. Also, I don't expect Rahman to ask for public opinion to select his singers. Of course not! Sorry - didn't want to cause a ruckus among Rahmanfans. Just an opinion on what is obviously a wonderful song!

