They appear to have become a great example of why the small businesses I run typically just walk away from any service we were potentially interested in using if we see a pricing page containing the word "call" but no actual pricing. If you're going to aim for high-touch enterprise sales, that's your choice, it's your business. However, the chances that you will then provide either acceptable quality of service or good value to anyone on the smaller end of the scale tends to zero IME, so it saves everyone time if we look elsewhere immediately. The problems start if it turns out that these companies aren't actually generating enough value to justify the enterprise-level costs either.

For example, say you're running a tool that allows people to quickly experiment with multiple versions of their web site, measure some quantifiable success rate for each version, and perform some basic statistical analysis to guide future changes and improve conversion rates. A basic but useful version of this tool can be implemented in a few days by one competent developer and one competent statistician; I suspect quite a few people reading this discussion have done exactly that. Polishing the tool might take longer and improve its utility somewhat, but it's not as though it's using some secret technique that no normal business can implement for themselves in-house.

At the mostly-self-service end of the spectrum, it might still be worth customers spending a bit of money on the pre-existing tool you make to do that job for them, because you're really competing on immediacy and convenience as much as technical capabilities. At the enterprise level, your competition could instead be some in-house team or some freelancer or agency being brought in from outside just to develop a tool directly for your customer. If they're potentially doing that at a cost less than just the first year of annual fees you're demanding up-front, and according to the customer's exact requirements, both of which seem quite plausible in a case like Optimizely's based on information in other comments here, what exactly is your sales pitch?