I don't follow this advice at all.
I think it is excellent advice for those who are starting out or want to keep investing simple.
Personally, I am not comfortable with the risk associated with this investing strategy. I keep an AA of 65% equities (2/3 domestic, 1/3 international), 25% well diversified fixed income, and 10% alternatives. This is my well-earned risk tolerance, and not really a recommendation for anyone other than myself.
I think the other place the 100% VTI (or similar) strategy could be improved is diversification. Sure, the bloggers shout from the rooftop that it's diversified. But dig under the hood a bit, and these funds are typically heavily weighted towards large-caps, and large countries. I haven't looked at VTI specifically, but it is a common issue among cap-weighted indices. Mathematically, increased diversification is the only free lunch in investing (per the efficient market hypothesis), so I prefer to increase this above the basic amount provided by a single index tracker.