I had a bmi of over 34 when I had both my kids. It was never made an issue of, not a word was said to me about my weight. When I had my son last year, he was delivered in a midwife led unit (there was a fully staffed labour ward up the stairs though, to be fair) and I was lucky to have no complications. In fact, he arrived 5 mins after I was first assessed by the midwife.
However, if theres scientific evidence to support this idea that very obese women are high risk (at no point was I ever told this by any medical staff), then a midwife led unit would be inappropriate - therefore I can see the point of this.
Many people are excluded from a midwife led unit due to being at high risk of complications, so really its not unusual, to be fair.