I don't remember that it was included by default. When they decided to add it, they offered it to existing customers and made it available for new customers if they paid more than the average price.
They made it clear:
"For all ~180,000 customers, this is complimentary."
and
"For new customers, we're trying an experiment: to unlock the Humble Bundle #1 inside of your bundle, just choose a price that is above average"
From what I remember, what I got (I think it was the second bundle) was only the second bundle. Then, after a few days, they emailed me to say "since you paid more than average, here's the first bundle as well, free of charge!".
But I agree, it wasn't from minute one.