Clearly the response here depends a bit on your interests. End user? Integrator? Consultant? Market? etc.
From an end users perspective our RFPs always include the "prove it" requirements. Examples would be bit rate calculations, storage calculations, network diagrams, design narratives describing redundancy etc. The theory here is twofold
1. If you are unable to describe your solution can you effectively deploy said solution?
2. In effort to eliminate confusion due to misinterpretation of the specification
Number 2 is a big one. To dovetail Brain above, check the box for "must have automatic failover server" then go on to describe the expectations/requirements is good, but no matter how well defined in the RFP narrative there is still the high likelyhood that something may be left to interpretation. Ask the bidder to back up their line item proposal with narratives, calculations and diagrams and you are now going to see how creative that Integrator is, get a better idea of their skillset and verify that your expectations were clear.
We have had some Integrators not bid our projects becasue of the upfront documentation we require for our medium to large projects ($300k+).