I'm really sorry to hear this!
DoubleMyCoins.com is a newly opened site that does the same thing. There is a warning about only sending from a wallet that allows incoming transactions.
MtGox has a ton of issues to worry about, like security, lawsuits, regulations and more on top of trying to run their business. Please understand they have tens or more like hundreds of thousands of users, so it's a bit hard to give each issue priority
Yeah it really sucks. All it would take them to prevent this from ever happening is one line of javascript, since SatoshiDice addresses are public and don't change (they also all start with 1dice).
I understand they must be new to this, but so far I've been told that they won't deal with my issue at all. I must be the only user who did not guess to hover over that one generic blue help icon on that page.
