No, but it's not people with IBS developing Fibro...it's people with IBS being diagnosed with Fibro...which was there, even if not a problem, before the IBS.
With me, I've had Fibro symptoms on and off since my early teens if not before. However, it was only when I got IBS and it got bad that the Fibro kicked in properly. It's like a vicious cycle...you have Fibro (or at least the Fibro genetic make-up) and that means you're more likely to develop IBS and if you do it makes it more likely that the Fibro will become a problem. SOme people (my Mum for example) probably have Fibro, but because they never developed IBS, or had a car accident or whatever, the Fibro never gets so bad to become a real issue.
Plus, these days, it's quite easy to get an IBS diagnosis whereas a Fibro diagnosis is more complex.