In Hollywood's defense, I'd imagine this is simply the IP version of the 555-XXX convention for phone numbers: so fools won't simply type whatever IP address they see on screen, thinking they've just Hacked the Gibson.
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498,438,559,990KG? What does that convert to in tubes?
You plonks just sparkle. We shine.
Oh, and to E.T.: I've got your ouch right here.