Actually they don't. It states both on Kickstarter and the RSI Tos that the game is subject to change and may be delayed. Kickstarter clearly states in the kickstarter faq (quote followsthis comment its a long read), It also states in RSI's TOS link and quote follows comment.
You can bitch and moan or hell even talk out your ass like Cutter or you can accept its pretty much like every other game out there in development thats in Pre Alpha. So its going to get delayed and yes content is going to change.
Its clearly stated on the Kickstarter faq and the RSI TOS what to
Kickstarter FAQ excerpt followed by RSI TOS excerpt:
What should creators do if they're having problems completing their project?
If problems come up, creators are expected to post a project update explaining the situation. Sharing the story, speed bumps and all, is crucial. Most backers support projects because they want to see something happen and they'd like to be a part of it. Creators who are honest and transparent will usually find backers to be understanding.
It's not uncommon for things to take longer than expected. Sometimes the execution of the project proves more difficult than the creator had anticipated. If a creator is making a good faith effort to complete their project and is transparent about it, backers should do their best to be patient and understanding while demanding continued accountability from the creator.
In addition on RSI website in the terms of service
RSI agrees to use its good faith business efforts to deliver to you the pledge items and the Game on or before the estimated delivery date communicated to you on the Website. However, you acknowledge and agree that delivery as of such date is not a firm promise and may be extended by RSI since unforeseen events may extend the development and/or production time. Accordingly, you agree that any unearned portion of your Pledge shall not be refundable until and unless RSI has failed to deliver the relevant pledge items and/or the Game to you within eighteen (18) months after the estimated delivery date.