I would find such language completely unacceptable for any service I actually paid for. At a minimum, the company should be liable to return any money paid if discontinuing the service, and should be required to offer a refund in event of substantive change in terms. (I'd accept prorating the refund, but that's as far as I'd go.) I would find even this insufficient for any service I was doing company planning around.
As it is these terms (if legal) would allow collecting money and then just skipping out with it. It's a Bernie Madoff guarantee.
These terms work just fine on sites where there is no payment. I get benefits from Google and StackOverflow and Facebook, and they sell my eyeballs to advertisers. There's no problem if either side just stops doing what they're doing. Once money starts changing hands, it's a very different situation.