I think the pattern wants you to cast on so it's stretchy enough for ribbing. Some cast on methods are too tight. I use the long tail and alternate cable cast on, and both work really well for ribbing. The videos are on this page.
There IS a provisional cast on for 1x1 ribbing on pg 29. in Vogue Knititng, but I've never used it... It looks a little awkward, and I think it's probablly not necessary. The alternate cable CO should work fine.