Did 37signals design the perfect Plans & Pricing page when they developed Basecamp? No. But while they continue to iterate, the competitors emulate. Borrowing the design guide for one of their most important pages. It's no surprise 37signals are killing it in this space.
Today there is no excuse. There's free tools to A/B test and optimize. User testing is now a whole lot cheaper thanks to tools such as Silverback. Paper prototyping requires.. paper. Look outside the category. More companies need to be leveraging these tools to innovate, iterate and ultimately lift conversions.
Update: Robert Dempsey has compiled a collection of Basecamp pricing screenshots since they started. Great to see how both the design has evolved over time, starting very simple, then getting too complicated and then reverting to simple. Cost structure has changed only once.