"going to a restaurant's home page will bring up a message, reading “I've got directions, hours, and more.” Clicking the message brings up a sidebar with the restaurant's contact information, location, reviews and an OpenTable reservation link" 
Yeah, but a data warehouse isn't supposed to have great response times. Data warehouses are for large, low-value sets of historical data that you don't always know how you want to use.
If you want to use data in real-time, you should be driving it from your transactional systems. Redshift and other data warehouse solutions are for doing reporting and dashboards, not triggering real-time reactions.
Most companies are generally more concerned about reducing their data warehouse costs than they are about improving the performance of their data warehouses. Many companies implement a multi-tiered DW structure to get a mix of the two, but the core driver is managing the cost of storing petabytes of data while keeping performance acceptable.