I'm the author of the article. At Monetate, we've chosen our data warehouses to maximize throughput, rather than minimize latency. That's where something like Redshift really shines, it's great a large bulk ingests and running large queries relatively quickly, but awful at running lots of small queries quickly.
On our busiest day last year, we ingested over a quarter billion page views across all of our clients' websites. I'm sure someone has made MySQL scale to that volume, but for us Redshift has been working great for a relatively low price point.
