Amazon actually encourages this. In amazon you do one of two things....1. you sell out of their catalog with their SKU's and make your product fungible with everyone else or 2. you get brand approval for your own brand and market it as you product.
Actually it agains their rules. Because it is clearly seen that those products are not brand. Duplicate listings are not allowed on amazon. And it is not allowed to put brand name into title. But yes we see amazon tolarates it.
There are many more eBay drop shipping operations than Amazon dropshipping operations. 1. Amazon will be much quicker to ban you and 2. I and many other people suspect that Amazon doesn't allow drop shipping operations to become too big before they shut it down.
I've created a thread about amazon dropshipping. I think it could be better if we discuss amazon there. Amazon allows dropshipping but not from retailers, only from specialized ropshipping companies.