The problem for all of us on the stand was that we have never found it problematic to jump horses XC without studs. In fact the general feeling among UKNHCP practitioners and clients is that horses slip less barefoot than in shoes, or at least have fewer problems with slipping, which may not be quite the same thing.
As Mark Johnson described several times over the weekend to interested visitors, the horse's limb needs to be able to slip slightly when it is subject to turning forces, otherwise additional stress is transferred onto ligaments and tendons. Obviously a severe slip, though, can result in a wrench or sprain (as Felix found out on Tuesday, I assume...).
There is no doubt that some riders feel more secure with studs in, but its hard to be sure how much this is a "placebo" effect. A rider of shod horses at one of Mary Bromiley's clinics agreed with Mary, that studs may not be as indispensible as they are supposed to be. She described when she thought she was riding her horse with studs screwed in. She didn't notice any loss of performance (believing the studs were doing their job) and it was only when she came to take them out that she realised she had done an entire intermediate event without them.
We will probably never know how much of the concern about barefoot horses not being able to use studs stems primarily from rider worry.
As for slipping, obviously this week isn't a great time for me to post thoughts about slippingafter Felix, normally surefooted barefoot horse extraordinaire, apparently came a cropper in the field(!). Nevertheless, all horses can slip from time to time, particularly on a steep wet field, whether shod or barefoot - a few weeks ago a shod horse came right down out hunting on a very tight turn on wet grass.
My own view is that the horse's own sense of balance is hugely important, and that as they develop both balance and proprioception, the problems of slipping are reduced.