You guys do bring up an interesting point. My personal opinion on this subject is that the bore circumference does not change, only gets distorted. Therefore it doesn't matter whether you use a ring grinding tool or this method, both will give you the same results as both grind the rings outside the bore.
I'm not really advocating this method as the best way to get the job done, this is just an option for those that want to build an engine but don't want to buy another $100 tool that they will only use once. I would not use this method if I had access to a ring grinder.