There's a truism you learn after a few years of investing in tech: Only platforms create sustainable value.

Witness MySpace, which News Corp. (Nasdaq: NWS) just sold for $35 million to advertising network operator Specific Media, according to The Wall Street Journal's AllThingsD blog.

In this context, "platform" refers to technology upon which outside developers can and usually do improve, adding value both to other users and the underlying platform, while creating switching costs where none existed before.

Need an example? Think of Windows. As soon as developers began writing code that users found worthy enough to adopt, Windows became a platform, sending shares of Microsoft (Nasdaq: MSFT) to the moon.

MySpace never really became a platform in the way Facebook has. Users install more than 20 million apps on Facebook each day. Game developer Zynga has created a multibillion-dollar empire primarily by embedding code in the social network.

How many installs does MySpace manage? Just more than 12,000 games a day as of this writing. True, the numbers don't match up because we're comparing apps to games, but the broader point remains: Facebook dwarfs MySpace, and News Corp. boss Rupert Murdoch doesn't like being dwarfed. That's why he dumped the site for a 94% discount.

Back in 2005, Murdoch's $580 million bet looked smart. Within two years, Yahoo! (Nasdaq: YHOO) would flirt with acquiring the site at a lofty $12 billion valuation, largely on the strength of a three-year $900 million advertising deal MySpace had booked with Google (Nasdaq: GOOG). But by January 2009, the equation had reversed. Suddenly, Facebook was not only bigger than France, but also bigger than MySpace.

Today, it's tough to call these two businesses peers. Therein lies the razor's edge of the cloud-computing revolution. For all the value that web-based computing and social media unleashes, there's little hope for any businesses that fail to create platforms. Call them the movement's remember-whens, or also-rans, or if cruelty is more your cup of cocoa, The MySpace Generation. Whatever you call them, don't ignore them. They may be lurking in your portfolio right now.

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