I had that wheel wax on mine but they went. Like d3fy says above they just rot from the inside - Mat C on here knows all the specifics but I think basically the problem is a combination of recycled metals and the fact they're designed for use in Japan etc where they don't salt the roads and the weather isn't as ****ty - think these are the biggest killers is that right lads?
I cleaned mine with car wash soap and water - if you do them regularly it's amazing how easy they clean - mine were absolutely ditched at the weekend and the car wash soap brought them up lovely, just banged a load of the autoglym stuff in there and it did the job a treat.
You can also put wax on the alloys - I've got some of the Alloy Wax but to be honest it never made a big difference to mine in terms of keeping them clean but I did apply it in the middle of the winter and I don't think it had time to set properly which is why it didn't work properly.
Will be putting a big dollop on my new alloys to keep them nice though