Workhouses - general question

I found one of the gentlemen I was searching for in 1871 and 1881 censuses  in a workhouse.  In both entries he is recorded as married.  I know his wife's name; however, she is not at the workhouse with him.  She was considerably younger than him...by almost 30 years.  Given this I have speculated that perhaps he was physically unable to work, but she still was....

I did find a woman on the 1871 census with the correct name, age and parentage... married to another man...?

Bizarre, but intriguing....Can anyone enlighten me as to the circumstances under which this would occur?

Jill (Canada)