The default nullability of RDBMS types is implementation-specific. Protobufs requires a lot of ugly workarounds for languages such as Java to handle the language's nullable types. You can't eliminate the complexity; only move it, and protobufs moved it in a way that punishes languages with nullable types. XML at least works via omission, but that doesn't handle the case of explicitly signalling "no data", which is a valid signal in many languages.

Concise Encoding does support IEEE754.