They most certainly are! That is-hard to keep clean and HARDER to clean.
I have found the best way to do it is to lift the bike up on my Jack and use a large soft sponge to get twixt the spokes, and warm water with lots of sudsy car wash in it.Get all the road and brake dust off and blow the wheel good and dry with my AirForce Blaster.Then run around every individual spoke up and down with a piece of polish impregnated cloth. Not forgetting to do the insides of the Hubs and of course the Rim.
Then clean off the polish residue with more pieces of soft cloth.The whole process takes me about 3 hours,but if you want the wheels to look good, you gotta put the time in----.
I have heard tales of Harley wire wheels rusting before their time as water gets inside the rim through the spoke holes.That's one of the reasons I use a warm air blower and rotate the wheels in an attempt to drain and get rid of as much water as possible.