Hi jleech,
I don’t know why they are changing it but they would be the most reliable source of this type of information anyway.
I would also keep in mind that if you aren’t able to find a relatively large number of people that have had a specific mattress for at least 5 years that also identify their particular body type and sleeping style that online reviews really won’t tell you much if anything about the durability or useful life of a mattress that uses good quality materials that would be relative to your own personal experience.
In terms of durability … a mattress is only as good as its construction and the quality and durability of the materials and components inside it (regardless of the name of the manufacturer on the label) and the most reliable way to assess the durability of a mattress or to identify any weak links in the design is by using the quality/durability guidelines in post #4 here.
A mattress that would be a durable choice for one person that could last them for many years may not last nearly as long for someone else (in some cases even a few years or less) depending on the many variables involved. There is also much more detailed information about the many variables that can affect the durability and useful life of a mattress relative to different people in post #4 here as well.
Phoenix
NOTE ADDED JAN, 2016: They have now introduced their new simplified choice mattress which has replaced their previous models and have also become a member of this site.