wine is i386 only. If your processor is x86_64 (most Intel Macs are), then yes, all wine dependencies must be installed universal. This is nothing new; it has always been this way.
MacPorts should have known to upgrade libidl to universal, since it is a declared dependency of orbit2. The only reason I can think of why this wouldn't have happened is if you had originally installed libidl with a MacPorts version older than 1.9 (which is possible, since libidl was last updated two months before MacPorts 1.9 was released).
