Chrono,
The numbers being quoted are not just from Launch day, but include numbers for that week. Please remember that Microsoft didn't just ship out 350,000 consoles and then STOP production of the X-Box. Microsoft has the manufacturing capability to pump out roughly 150,000 consoles per week at full capacity. Assuming they are at full capacity, that means the week following launch, Microsoft sold 150,000 pieces. Actually if you want the EXACT numbers, according to CSFB here they are:
First 3 days (November 15th-17th): 370,000 consoles sold
Next 7 days (November 18th-24th): 186,000 consoles sold
Combined totals: 556,000 consoles sold
With a tie in ratio of 2.4 that translates into 1,334,400 games sold for X-Box.
Thats how 500,000+ X-Boxes can be sold as of November 24th.
Given that GameCube shipped 3 days after X-Box, the numbers are pretty close in both hardware and software sales if you consider that X-Box has quite a few more launch titles than GameCube does.