“Apple’s App Store Soars Past 300,000 Apps,” reads the headline posted Thursday on the website ReadWriteWeb and picked up by SlashGear and GottaBeMobile.

Sound familiar? Perhaps that’s because two other prominent tech news sites — MacNN and VentureBeat — reported that Apple (AAPL) had passed the same milestone nearly three weeks earlier, on Oct. 16.

Who’s right? As near as we can tell, none of them.

According to two app-tracking sites that actually go into the store and run daily headcounts — 148Apps.biz and AppShopper.com — the U.S. App Store is still roughly 10,000 apps shy of the 300,000 mark.

The discrepancy arises because Mobclix, the source of the Oct. 16 reports and Distimo, the source of Thursday’s, are analytics firms that count all the apps that have crossed their radar, whether or not they are still available for download. [NOTE: Distimo disputes this. See comments.]

By that measure, the App Store is approaching 350,000, according to our two app trackers:

. . .

Does any of this matter?

In fact it does. Apple and Google (GOOG) are locked in a race for the hearts and minds of developers. There are a lot of interested parties — many of them investors — reading these reports closely to see who’s winning.

The least we can do is get the numbers right.

UPDATE: Italian blogger Fabio Zambelli of setteB.IT points out that in an Oct. 26 press release about the opening of its Chinese App Store, Apple refers in the fourth graph to “the world’s largest catalog of apps with over 300,000 apps.” The difference here is that Apple is counting apps that appear in overseas App Stores and not in the U.S. If the U.S.-based app trackers could figure out a way to count those, the total number of apps approved worldwide would be well over 350,000.

See also:

• 300,000 Apple apps? Not so fast!

[Follow Philip Elmer-DeWitt on Twitter @philiped]