Nope, it is an error in Gatherer. Being printed in Conspiracy does not make it standard or modern legal, unless that card has been printed in a standard or modern legal set (and Conspiracy does not affect that). And in case some player is confused, you can point them to section 3.6 of the Magic Tournament Rules:
Players may not use errors or omissions in Oracle to abuse the rules. The Head Judge is the final authority for card interpretations, and he or she may overrule Oracle if an error is discovered.
So no, cards like Swords to Plowshares are still not legal in Standard or Modern.
Nathan Long
Wizards.Com Boards NetRep