Oh, we have about 10 network machines at the office running 24x7,
I think you overlooked the hardware redundancy issues I spoke about.
If you're sitting around at 3am and an OC3 card drops dead you can't just pick up a spare and most people don't keep spares of $38K cards laying around and it's usually a specialty part that takes a long time to get replaced.
If you prefer to own instead of rent, colo is an option which avoids getting your own internet provider, just your server hardware.
Then again, when you're sitting around at 3am and the hardware fails, you're on the hook to drive to the colo to fix it which is why leasing theirs is always better IMO.
Now consider what would happen when you and your crew are at some tradeshow and your roll-your-own server network goes belly-up, like during the middle of PubCon.
How much fun would THAT be? :)
P.S. I've been that guy up at 3am many times, not fun.