Lost in the discussion, I think, is the aggravation of having to go buy and then schlep around RO water every time you want to brew. For me--YMMV--that's a pain, and if I were able to get it in large enough containers, well, I don't want to be carrying that.
I have an RO system at home w/o the pressurized tank. I have a 7-gallon aquatainer I use to fill my BK at the start of every brew, then I immediately set to refilling it for the next time. I never have to move more than 3 feet to get that water, and it's always there and ready for me. No having to plan around having to go get that water. That's important to me--YMMV.
I don't just use that RO water for brewing; I have a Keurig coffee brewer in my office and I bring RO water in 1-gallon jugs to feed that. RO means no (or virtually no) buildup of scale over time and thus no having to clean it out. So I have that benefit too--and no going to the store to get that, either. At any one time I'll have a 7-gallon aquatainer full of RO water, plus anywhere from 5-13 1-gallon jugs of RO water waiting for use in brewing or for my coffeemaker.
There is the downside of a system--there's up-front cost, and the water isn't completely free. But for me, the time savings and convenience are worth it.
Others might have different parameters in deciding what works best in their situation. And in the end, we all get to apply our own interests and values, and make our own choices. Nothing wrong with that.