That is correct. Currently, the only two values allowed are 2.0 and 3.0, minor versions are not supported. If no version is specified, the ePub 2.0.1 specification states the document should be treated as an OEBPS 1.2 document.
From the ePub 3.3 documentation:
The version attribute specifies the EPUB specification version to which the given EPUB Package conforms. The attribute MUST have the value "3.0" to indicate compliance with this version of the specification..
While the ePub 2.0.1 specification states:
In addition, to be processed as an OPF 2.0 package, a version attribute with a value of 2.0 must be specified on the package element. A package element that omits the version attribute must be processed as an OEBPS 1.2 package.
I find that searching for version="3\.0" works fine for me and allows for those files that add additional bits or rearrange the items in the <package> field.