This restriction, which is not imposed by most computer languages, is necessary because POV-Ray allows mixing of float and vector expressions. Without the parentheses there is an ambiguity problem. The operators and their precedence are shown here. All relational operators have the same precedence. The result is always boolean.
All logical operators have the same precedence.
Note that these are not bit-wise operations, they are logical. The operand C is boolean while operands A and B are any expressions.