So you got the offer and you're packing your lunch for your first day and you get a call.  And the company says thanks but no thanks. Can they do that?  Sure.  Unless you had a signed contract - which most people don't - and which probably has some clause on page 23 that says that they can.
And why would Mr. Employer do that?  Money.  Bad results or even worse?  New directive from a big cheese?  Change of executives means you are not the flavor of the month anymore.  All kinds of things.

What can you do?
Keep in touch.  Keep communicating.  Meet up with the boss before your official start date.  Visit the company ahead of time if possible.  Keep researching the company.  And if something doesn't make sense or looks strange then ask questions - lots of questions.  You may not be able to do anything but you can be prepared.  If things look dicey or risky at a company then you can start looking for a plan B, hold back on any big plans like moving or buying a new car on the strength of the job or just be emotionally ready.