Alex Smith has been very good for the San Francisco 49ers this season. Sitting at 7-1, he really has to be, though "very good" has different definitions for different people. He's not out there every week throwing the football like a gunslinger and putting up 300+ yards with three touchdowns, but he's winning the game with accurate throws to keep the offense moving. It really should be undisputed that Smith is playing above-average, winning football - but because it's not flashy, he's not well-regarded by many.
According to the Press Democrat, New York Giants defensive end Justin Tuck had some things to say about Smith's play. Tuck said that Smith was playing "decent" and that he was being put solely in a position to not lose games. Tuck was both complimentary and somewhat insulting, in a weird way. Most would argue that Smith is playing much better than decent, and though it's true that he's not being given a chance to lose football games, that's not his "only" purpose out there.
It's true that Jim Harbaugh is limiting Alex Smith, but that has more to do with the fact that running back Frank Gore needs the carries and a great defense keeps this team in constant good field position. Tuck notes that the 49ers are going to run the ball in field goal range, and that's not necessarily true. The play-calling seems evenly distributed in field goal range, and Alex certainly has come through in those situations before.
Did somebody else throw the 30-yard touchdown pass against the Washington Redskins to Bruce Miller? Or was it somebody else who hit Delanie Walker on fourth down just a few weeks ago on a slant route to win the game? The 49ers aren't limiting Alex Smith to keep him from "having to win the game," they're simply running an offense that works - and they most definitely are confident in Smith's arm in the crunch time.