The number comes from the combinations of the initial block reward (50 coins), the target blocks per hour (6) and the halving period (4 years).
Ah, that makes more sense now.
And here I thought it was because when you divide the starting number of coins generated by the number of blocks before the coins halve and then multiply by the current recommended transaction fee you get the answer to life, the universe, and everything:
(210,000 / 50) * 0.01 = 42
May you be touched by his noodlely appendage.