I can understand, for sure. I was in the same place myself ~6 months ago, as I said.
As for why they won't step in and make a statement, my guess is that they simply don't have the testing procedure in place to ensure they don't get too many returns, and can't justify the cost of the testing or the returns, both of which cost money. They likely can't pass the buck to the panel manufacturer -- I wouldn't be surprised at all if they have a contract for the dead pixel policy that allows them to do so, but weren't aware of the tinting issue ahead of time and didn't get that contracted, so now Dell themselves would have to bear that cost.
$600 isn't close to professional monitor pricing -- it's an expensive consumer monitor, but a consumer monitor nonetheless. Pro monitors of this size can easily run into the multiple thousands of dollars.
You get what you pay for. At $600, I've found it to be quite a lot..