Plus an architecture that is robust.
In my experience, good dedicated servers practically never crash. You might lose a HDD every few years, but that is not urgent to fix if you have a good raid.
Avoid most cloud services. Heroku, Rackspace, AWS all had much more outages than Hetzner. Plus they'll sometimes force reboot or force migrate ( =pause) your instances.
So if you go cloud, you'll need failover, distributed database, all that messy and complicated stuff. If you go dedicated, it's much easier and you only need to keep that one box running.
Plus, honestly, would your customers really mind if you're offline for 5 minutes? My dedicated hoster also has a service where they will monitor standard services like Apache, Postgresql, Rails for you and restart as needed. They have 5-10 minutes response time in my experience and I belive its good enough :)