It's not a dumb question at all, it's a serious and unanswerable one. Well, there are answers-- but they involve user-agent detection.
This is not completely hopeless with tablets, because there's a finite number of them. At least this week. But it still means something more complicated than putting an @-rule in the main CSS. Now you're looking at on-page scripting, or something at the server level that checks the UA and-- at a minimum-- serves up different stylesheets depending on UA. Changing stylesheets is a heck of a lot easier than maintaining different versions of a page, though of course it won't work for all pages.
A tablet doesn't count as "handheld". That is: it doesn't consider itself "handheld"-- and in this case, the device's own opinion is what matters ;)
Is CSS 3 doing anything about this? Seems like it ought to...