Agreed, Pennington can definitely take us all the way, but like you said, he can not do it by himself.
Some treat Pennington like he is just an average quarterback. He is arguably one of the top 10 starting quarterbacks currently in the game. Sure he doesn't have the strongest arm, but he is smart and knows how to take care of the football. He had great statistics last year and was exactly what this young offense needed.
nosleep made a great point about the Buccaneers winning the Super Bowl with Brad Johnson. Another good example is that the Ravens won the Super Bowl with Trent Dilfer. Pennington in my mind can have more success with this offense then either of those two with their respective offenses.
As long as Pennington stays healthy, which is no guarantee, yes he can take this team far. He needs help, but every quarterback in this league needs help for their team to go far. Ben Roethlisberger is a good quarterback, but he never would have won two Super Bowls without a solid defense and a good running game. Same goes for the likes of many quarterbacks such as Eli Manning to name another.
The team will probably have an offense with more passing firepower with Henne at the helm, but there will probably be more turnovers also. Not a shot at Henne, but Henne is more of a risk taker then Pennington. Pennington will turn it over less, but the offense may score less. Henne may turn it over more, but they may also score more touchdowns. They are two different players and both are good options for this team.
If Pennington can stay healthy for a second straight season and lead this team to another playoff appearance, he earns the right to at least come back next year and compete for the starting job. Henne by then will be more then ready to be a starting QB, but you just don't discard a good quarterback like Pennington(assuming he has another big year and stays healthy). The Jets learned the hard way last year when they chose Favre instead of Pennington and they looked like national fools for doing that. Not just at the time of their decision in August, but in Week 17 when Pennington outshined and outclassed the Jets to win the division title and eliminate the Jets from playoff contention.