Homebond is not a legal requirement. It is a private structural warranty scheme, but many lenders require a recognised warranty on a newly built home bought from a developer, and buyers' solicitors routinely ask for one.
Statutory protection comes from the building regulations and building control certification, not from a warranty. A warranty is a commercial product that adds an insurance layer on top.
For a developer-built house, the absence of a recognised warranty will usually be flagged by the lender. For a self-build being sold later, buyers rely more heavily on the certificate of compliance on completion and professional opinions.