1. Paying for a Blackberry does not entitle you to this service, just like paying for a PS3 doesn't entitle you to free PSN connectivity. They are only compensating people to maintain customer relations, not because it is compulsory.
2. If you were running your business and solely relied on RIM email, you would be an idiot, and not a very successful business owner.
I bet RIM don't rely on their own service. You never use any sort of communication method as your sole use of contact, everyone has a redundant/secondary communications method. If they don't, that's not RIMs fault.
Electronics are not infallible and they are not 100% reliable. You always need multiple communications options just as you would have a back up server in case your mainframe went down.
They rely on BB servers...