[oarsinsync]

> They aren't, as far as I know, drastically undercutting the prices of their services to levels that aren't sustainable for other companies to compete.

Difficult to compete with free on a large scale, you can only compete on niche audiences at that point. Gmail feels like a good example here that effectively drove out most of the other competition's relatively limited free tiers for personal users, leaving only larger businesses and privacy-oriented individuals to continue to pay for email.