Why McLaren starts 2003 with the old car

[Steven]

David Coulthard has repeatedly warned McLaren that they would have to come up with something totally new and revolutionary to close the gap with Ferrari (that was 108 pts between Coulthard and Schumi at the end of the season).
"We have a lot to do in the wintertests", Coulthard told. The new car is being postponed to give Adrian Newey, McLaren chief designer, the chance to test and design the car optimally, to make Raikkonen and Coulthard possible to win races.
After last year's Ferrari came out three races after the start of the season, this seems to become a tendency, now with both McLaren and Ferrari (again) postponing their new contender.

[SpeedTech]

Well postponing their new contender earlier this year helped Ferrari. Extra time to test
It dosen't surprise me that another team is starting to follow the trend. Just look at Ferrari this year, they dominated. Why ? because they made sure their 2002 contender was reliable. reliablity win's races.
"To win a race....you first must finish it"