Pow functions with negative exponents or bases are not necessarily portable across platforms and devices.
This is because many power operations on video cards are implemented as exp2(log2(B) * A). This does not support negative numbers in a predictable way. Different platforms will handle negative or zero cases differently.
While Shader Graph aims to be as portable as possible, there would be a performance penalty to hide this problem. Users can handle this case by preventing negative values to show up in content or by handling such cases within their graph as they see fit.