That post does actually explain it, but let me ask you this question. When you say you are comparing supplier prices here with eBay prices. What prices are you comparing?
For example, are you comparing dropship prices against eBay sellers who are wholesale buyers or even worse, wholesale sellers?
If you are doing something like that, then of course the eBay seller is going to be cheaper, you can't possibly expect them not to be. Consider this, a dropshipper is buying one item at a time and a wholesale buyer can be buying as many as they want at a time, 100, 1,000. 10,000 or whatever. The more they buy, the cheaper the per unit price they get.
If you want to compare wholesale prices, you will need to speak with the wholesaler direct to discuss their prices on a volume equation to get accurate numbers that you can then compare against.
That's how retail business works, you can't possibly expect to get the same price from a supplier when you are buying one item, compared to a person spending much more money with them and buying 100 more. So saying you are comparing prices doesn't really amount to much at all, it's what are you comparing prices with?