That is mostly true. I would still go into a snowboard shop and try on a few different brands just to make sure. you dont want to buy a pair online then when you get them your toes are getting smushed in. I ware a size 10 shoe but my last pair of snowboard boots were a 9.
I'd definitely go in the store to try on some boots before buying any boots online. Everyone has different feet and there is no way to tell if a boot will be comfortable or not until you actually try it on. For example, when I went into a shop a few days ago to try on some boots the shop worker gave me a pair of Burton boots to try on that are his personal favorite. They were my size but they weren't comfortable on my ankle. If I had ordered them online I would have had to send them back because there is no way I could ride those all day and be happy. Hopefully the guys helping you out at the shop actually know a thing or two like mine did, he really helped me understand more about boots.