Sorry, but I'm going to be a party pooper here. I'm certainly not in the "CIO club", but I do let my DD cry for short periods (5 mins at most) before I see to her, as long as I KNOW she is well and isn't sick or hurting.
It might not be the case with all LOs, but I can tell by my DD's cry whether she is sick/vomiting or just crying to self-soothe. A good vomit is certainly distressing, so I can understand your concern. My DD definitely has a different cry if she is sick (more high-pitched and urgent) and I really can tell in her cry if she has vomited.
I can't understand the logic in letting children cry indefinitely without checking on them, but from experience I know that letting them cry for short periods of time (before the cry escalates) and going in to reassure them at regular intervals certainly does no harm. This mentality has kept me and DH sane for the past 2 years, and has given us all excellent undisturbed nights of sleep.