Your argument is logical, however it assumes that a critical mass of customers will apply the same cost-benefit calculus using the same assumptions. Right now that is clearly not the case.
Most SMEs view expenditure on IT, including security, as a cost to be minimised. This is a long term trend. If you want to charge a premium it is important to differentiate as much as possible from commodity solutions. I'm looking at the Cyberbiz brochure now and I see little that is not standard on dozens of cheap, competing products. The only standouts are the 24x7 monitoring and (for $999 a month) incident response. It is unclear what the actual business value is here, so it is likely to be heavily discounted in the minds of prospective customers.
Looked at another way, managed security provides two benefits. One is defence and the other is reduction in liability. Cyberbiz arguably provides no better defence than cheaper competitors, and any incremental reduction in liability is speculative. This lies at the heart of their poor sales.
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