Seems to me that the fuss is about the numbering system, not about J Crew extending its range of sizes, which brings me to my point--why does anyone care about the numbers?
I get that ordering online is difficult because it's hard to figure out the correct size but we've been around this "standardization" topic several times on the forum, and for what it is worth, I'm GLAD that there isn't a standard size X based on the dimensions of the "average woman". My IT proportions make me the exact opposite of the "average" pear/hourglass frame so a standardized size 10 across all companies would mean I'd always be faced with wearing clothes that billowed around my non-existent hips, strangled my largish waist, and refused to button around my chest. And as for sizing variation within the same company, much of that depends on how you like your clothes to fit. Some of us want our clothes to show the outline of our body, while others prefer a looser, drapier fit. Even those of us who like drape differ on exactly the point when the drapey/slouchy turns into baggy. So whose definition of fit and length do we use to "standardize"; my vote would be for my 5'7" length and preference for a loose, drapey fit, but I suspect some of our more petite members might object to drowning in their "standardized" clothes. As for those for complain about how today's size 2 used to be a size 8, who cares? Unless you are interested in vintage clothing, what is the point of knowing what your dress size would have been fifty years ago?
OK, I'll stop my rant here, but I think it's time to break out the champagne and celebrate when any company extends its size range to accommodate more people. Personally, I think companies ought to be required to reverse their numbering systems; under my proposal, size 000 will become size 20 and the current size 20 will become size 0000. Even when the inevitable complaints start about how terrible it is to be thought of as a 0, it might still be a refreshing change as to which group gets to feel upset at not having their own number and whose size will be inevitably at the bottom of the stack.