So if I only have one item left in stock, I should not be allowed to list it on two seperate advertising formats?

You can list it in as many places as you want as long as one of them isn;t ebay (or incidentaly QS, they have the same policy). You cannot pick and choose which polcies you choose to abide by and which you wish to ignore and I doubt if ebay would have restricted your selling for just one policy breach.

As for being pro ebay I am neither for or against ebay, they are a tool I use to sell items and as I choose to abide by the rules I don't have a problem with ebay doing something about those who don't although as noted their policy does appear to be slightly selective, perhaps the number of times a seller complains has something to do with it!