Well, big companies sure. We for example have several cages with multiple racks in several datacenters around the world but would never host out of our office. A company I consulted for had ONE datacenter in-house but several co-locations. So, unless you are willing to spend BIG BUCKS on hardware (firewalls, load balancers, servers, backup systems, constant server updates, hardware replacement) you are best of just getting hosting for a few bucks a month. Kind of like comparing a seed with a tree, but hey!
Actual hosting a web application over a DSL connection for something that you use to make money with… um… I wouldn’t recommend it.