No, accelerating payment due date for a debt in event of default is a pretty standard contract boilerplate.
>
> As I understand it (lawyers please correct me if i am
> wrong) penalties for breaking long term contracts as a
> result of one-sided changes of contract terms can be fought
> on the grounds of the promissory estoppel doctrine (i.e it
> would be unjust for a company to reneg on its promise of a
> certain terms of service and then charge me cancellation
> fees if I cancel the service.)
Promissory estoppel is a sort of substitute for an argument from a contract; you can argue in some cases that the technical terms of contract formation were not satisfied, say no writing where a writing was required or no consideration, or something, but the promisor is nonetheless liable if he fails to keep his promise because the other side relied on it, he knew and expected they would, and it would be unjust (tick off the judge) not to enforce the promise. It is a doctrine that is normally invoked as a last ditch hopeless hail-Mary pass by people who don't have contracts but have suffered losses because of broken promises. It's not very often a winning move and it's hard to imagine a judge allowing it to be applied when there was already a clear existing contract to interpret.
Now the situation you describe is not actually PE but material breach: if the company reneges on a key term that matters, a deal maker/breaker, in a contract that exist (PE is trying to make a promise that is not a contract enforceable in court) then you have grounds to argue on various bases that your obligations under the contract are in whole or in part discharged or excused.
A hypothetical: If a contractor walks away from a job, leaving your kitchen half finished, you probably don't have to pay him for the work he didn't do and you might even be able to make him pay for getting the rest of the job done at market rates, plus damages for loss of use of your kitchen in the interim. You'd still probably owe him for the work he did do.