2-year rule?

Has anyone heard of a 2-year rule when it comes to living abroad and paying taxes?  We first heard the rumor before we left for the UK from a British co-worker of my husband who stayed exactly 23 months in the States and said because he there less than 2 years he received back all the taxes taken out of his paycheck.  He told us it works both ways and suggested we stay less than 2 years in the UK to take advantage of the 2-year rule. 

Then just recently a Chinese co-worker of my husband's told us the same thing and that everyone he knows returns to China within 2 years to get all their taxes back.  Is there any truth at all to this?  I ask because my husband has become very bored at work (his work permit is the reason we're here) and is seriously contemplating moving back to the U.S.  I'm happy here though and am not ready to move back, but he's using this 2-year rule tax thing as an argument as to why we should return.  I tried looking it up on the HM Revenue & Customs website, but couldn't find a definitive answer.

If your husband was posted to the UK by a non-UK employer for an assignment intended to be for less than 2 years and he actually spends less than time here he could claim detached duty relief.

Alternatively, some treaties exempt some kinds of income (usually teaching) if the job is for less than 2 years.