Its not about being as good as Xabi or even close to it, Marchisio isnt even CLOSE to being the same type of player. He is not a calm slow regista that effortlessly sprays around balls all over, not at ALL.
You havent seen him if you think he is that type (you havent seen him either if you call him not mobile or hard working as someone did above), even if his passing is quite good (more short range then long range). Marchisio is more of an unique allround dynamic CM, does box to box quite well, is quite mobile and hardworking with some well needed tenacity in DM work, and overall quite skillfull tools to do more then one task of a central midfield role (was originally a forward ala Del Piero in younger days, so some of that technique and skill set can be seen in the mix).
Again Cigarini is a Xabi type, Marchisio ISNT. Not the same type of ball game at all.
If you havent seen him in Empoli and Azzurini as I have, then maybe this 1 minute clip can tell you a little of his A game:
http://uk.youtube.com/watch?v=hkvq-bljy_Q