Not to mention that the original context for the comment was apparently to do with being separated from his daughter for extended and often indeterminate periods of time for work. In that sense it's not quite as ridiculous as it sounds at first blush. When asked if he felt his work was otherwise comparable to active duty, Cruise apparently dismissed the suggestion as being utterly absurd.
TMZ, bastion of journalistic integrity, of course ran with "Tom Cruise says acting is like being in Afghanistan" because it makes for a better headline.
FTR, I couldn't care less either way, the guy's still a bit of a fruit loop regardless.