Except...the indemnity policies are usually pretty worthless, but the lawyers don't read them, and the mortgage companies simply accept the lawyer's Report On Title, and accept the indemnity...but that doesn't release the lawyers from blame if it all goes wrong.
NHBC is required if there isn't an architects certificate on a new house (there are other schemes) and the mortgage companies require one or the other, but from personal experience I can say that making a claim is a long, tortuous and seldom fruitful experience. Sad to say, the majority of new-builds are very poor in so many ways...that's what you get when you pay bottom-dollar to the trades to keep the profit up.