I've found that spelt items are much harder to find than rice-based items. I can find rice pasta in Trader Joe's, rice pasta and rice flour in Whole Foods, rice flour and pasta in the local supermarkets; but only Fairway consistently has a wide selection of spelt products (while also carrying the compliant gluten-free products.) Shop-rite sometimes has whole spelt flour, but not always, and they never have any other spelt products.
I'm guessing there's less of a market for spelt products in North America as a whole; people who know little about nutrition will go ahead and eat the wheat (not needing spelt), while those who need to avoid gluten won't eat spelt anyway. This makes spelt a bit of a "specialty" product that's not easy to locate. For those who can safely eat spelt, using spelt products means that foods have a better texture than any gluten-free item, and may make the difference between sticking to BTD or deciding it's "too hard to follow."
I can't personally eat spelt but I do buy a lot of spelt flour and bread for my kids.