Will I have an answer, or just more questions? :-)
Let's say, for the sake of argument, that my house gets really dry in the summer, and is relatively humid in the winter. There's no way I'm going to run the humidifier in the summer, it's hot enough as is, the A/C has just enough oomph to keep the house cool without making it fight with a humidifier too. So I still need to find a flooring solution that can handle the humidity swings (which sounds like I need to avoid solid wood and also solid grass).
Or, what if my house isn't that different (humidity-wise) in winter vs. summer. Then I guess we say the problems I've seen with my bamboo are not with seasonal variations, but rather just that the bamboo wasn't fully dry when it was installed, and that installing bamboo in the future might do just fine ... except that it's difficult to say when bamboo is really fully dry (has reached equilibrium moisture content), so I run the risk of having the same problem with the new floor, so I'm still better off avoiding bamboo.