Why 140 characters?

I posted a query to Twitter, asking why twitter had a limit of 140 characters. Within seconds, both @intellagirl & @sclater had pointed out that it was based on a standard SMS – though I still wasn’t entirely sure – as I’d thought SMS was 160 characters (which Wikipedia confirmed) @josiefraser then supplied me with 140 Characters » How Twitter Was Born – it’s from the 160 SMS characters – but they cut it back to 140, so that a user ID could prefix the message.
Twitter had quite a few mentions in the Guardian/Observer over the weekend … seems there’s been 103 so far this month, that’s 24 in the Guardian, 7 in the Observer & a further 71 on the website. I’m guessing that means “71 in addition to the repeats of the paper content”. Can’t work out how to have a “not” in the search – I could filter to one of the three (Guardian/Observer/online), but not to “not online” (or, I guess “Guardian & Observer”)