I think 'natural solution' is a play on words. My understanding is that all the search engines (including Google) spent many years figuring this out, failing many times along the way. PG's patent on Bayesian anti-spam is another example of something which seems obvious in retrospect, and now everyone does it.

'Natural' to me means a product or feature which just fits perfectly within the system. A natural solution is the most valuable and often hardest to come by. They also tend to seem incredibly obvious in retrospect, and yet examining history will demonstrate that others suffered for years for lack of that exact functionality.

For example, the intermittent wiper, or the teleprompter, or maybe even the paper clip. It's the ideas that seem the most obvious in retrospect which need the strongest patent protection. But only if you can show it's novel.

One way the patent office will let you demonstrate something is 'non-obvious' is if you can show something is both novel and actually solves a large existing problem in the market. The novel, simple, elegant solution to a large problem is by definition non-obvious, or else someone else would already be doing it.