No, the HPV vaccine is not necessary. However, it surely seems like a very good idea.
The vaccine is not necessary because there are other ways to prevent the problems that the vaccine is meant to protect against. Specifically, if both a person and their sexual partner are strictly monogamous throughout their lifetimes, they will not be at risk for contracting the virus that the vaccine is meant to guard against.
In this sense, the vaccine is not necessary. However, it seems like a good thing to have as a back up. Even if a person is sexually faithful, there is no guarantee that his/her partner will be. It would seem like contracting HPV would be a pretty high (since it can cause cancer) price to pay for choosing to trust the wrong person.