Is the timestamp in the genesis block relevant? Bitcoin's genesis block contains this text published in The Times on January 3rd, 2009:

The Times 03/Jan/2009 Chancellor on brink of second bailout for banks


According to the Bitcoin Wiki, this guarantees that the block was only created after this date.

What would be the problem of using any other random quote?
The newspaper quote proves that Satoshi did not mine a large number of blocks before the public announcement of Bitcoin on January 10. The block chain creator could for example create a chain of 1000 blocks before publishing just the first one. He now has a head start for mining and can invalidate the public block chain at any time by announcing the blocks he kept secret as long as his chain is longer. The block headers contain timestamps but these can be manipulated if no one else is verifying the blocks.