I think its a very subtle thing actually. The uccharan (pronounciation) in Hindi is a bit tricky due to our Sanskrit legacy. Like we have two empashis points on vowels, we call it "Matra". I am no expert in Hindi or Sanskrit, but if you look at the most Sri Lankan names that start with Pronounciation V are actually spelled with W. This is because in sanskrit the emphasis on Vee would be a tad lesser than say in Hindi. I think some people use The half-matra or the "Lakar" as it is called in Sanskrit to make the difference in pronounciation.
For exampls. A name like Vijay in Hindi would be pronounced Ve-J-aye. However, the same name in Sanskrit would be prounced a bit quicker with emphasis on the opening V and extending the ending. Its actually very hard to explain in text but from the limited knowledge I have in Indian Literature this is the most logical reason why some use V instead of W.
For quicker and perhaps more correct pronounciation.