More or less the same for Steam. You aren't guaranteed anything.
MS has pretty much said they have the right to take games off XBLA and not support them at any point they want,
Heh, on that note, ever tried to deal with Valve support? It's not pretty, usually.
and they have also said its not their problem if your system dies and you lose your games.
You get the rights spelled out in the user/subscriber agreement and purchase details. You get access to the content, according to the terms of the subscription contract. What, do you think there should be, like, a federal law that states that all digital content delivery services should be forced to provide indefinite downloads? Infinite downloads are either a feature of a particular service/company, or it isn't.
but I do want to know that I have some kind of rights over my purchase and that a company must at min continue to provide me access to what I have paid for indefinitely.
It's not about "rights," like, as if we were talking about civil rights or something here. It's about the terms of private purchase agreements/contracts.
Again, not that different from a CD. You don't get a guarantee of permanent access to the contents of a CD or DVD, either.
Hah, is that so? That's fine, if that's been true in your experience, but you should hear how they treat the developers they publish for:
The maker StrategyFirst treats their customers right - SO FAR.