There are several possible solutions, though some are more likely than others taking into account the extended rules of probability from other worlds.

[Oh yes, the 'can you deduce' game, he likes this one. He always wins.]

The suit acts as a sort of portable iron lung, assisting in illness or infirmity, and he cannot survive without it. No-- No, that doesn't make any sense, he could take off the armour in that case, it would merely be inadvisable. It can't be welded on, someone would just cut through it.

[He hums thoughtfully.]

He is the armour. A robot?