I do not think it is so much can't as shouldn't. Best practice dictates assigning a package to your classes. For quick tests, I often create java bean classes with no specific package. Hence, they become part of the default package.
A type-import-on-demand declaration (�7.5.2) imports all the accessible (�6.6) types of a named type or package as needed. It is a compile time error to import a type from the unnamed package.
The java code beind the JSP is going to have to do an import for your bean insn't it... and the specs say that an import from the unnamed package is illegal. i.e. all Beans must be in packages.