> There were also far fewer users to really discover the nasty edge case bugs.

If you consider why a company makes something reliable or not, it's a relatively simple formula:

    = Number of Users x (Benefit of Getting it Right x Probability of Getting it Right) - (Cost of Getting it Wrong x (1 - Probability of Getting it Right)))

As the number of users in any system increases, the cost overall cost of getting it wrong also increases. You can then devote more fixed cost resources to improving probability of getting it right.