Apple on Tuesday announced that it has sold 3 million iPads in 80 days. The announcement comes only three weeks after Apple announced that it had sold 2 million iPads in less than 60 days.

In and of itself, the 3 million mark isn’t a meaningful number. But it does offer an important indication for Wall Street: Apple’s selling iPads faster now than before, having blown through another million in three weeks. It’s also an opportunity for Apple to thumb its nose once again at analysts and technology writers who expected the iPad to flop, or at least to peter out long before Apple sold 3 million units.

It also helps Apple to reassure iOS developers supporting the iPad that they’re working with a growing user base. The number of iPad apps has more than doubled since Apple’s last announcement, also. When Apple announced it had sold 2 million iPads, it counted about 5,000 iPad-native apps. Now the company says that more than 11,000 iPad apps are available.

Apple began selling the iPad in the United States in early April. Shipments began in Australia, Canada, France, Germany, Italy, Switzerland and the United Kingdom this past weekend. Apple also expects to ship the iPad in nine more countries starting in July, with more countries coming on board later this year.

The news comes on the cusp of Apple’s release of the iPhone 4 in the US, UK and Japan – that rollout begins on Thursday, June 24, 2010. The new iPhone 4 is the first iPhone to ship with iOS 4, a new version of the mobile operating system which the iPad will get later this year.