Or maybe they learned from the Pre release. They didn't have enough supply to meet the demand and from the looks of things the Pre owner is the number one defector to the EVO, so their stockpiling to meet the demand.
You're right about non-Palm devotees ready to switch to something else. I just like to add that I think the Pre release was more about selecting the wrong hardware than anything. WebOS is decent, but Palm has faultered with manufacturing since before Pre's release. I think Sprint took the risk because Palm had a decent track record, and the invesment risk to get an exclusive phone was negligible. It just didn't work, and it was probably a blessing that sales for the Pre weren't astronomically high.
The Evo's a totally different ballgame. Sprint, HTC, Clearwire (now Sprint majority-owned) and Google/Android stand to leap forward with this phone and Wimax. Pre was a niche platform with limited apps and buyer potential to grow. I always liked webOS and Palm's PDA products, but it was predictable that Palm lost it's edge as an OEM through the many unsuccessful other products they tried.
But to your point, Palm never had the ability to respond to early demand for the Pre. By the time it did respond, the demand had dropped significantly. By September just 3 months after launch, the sales figures started to go unexplained. Quality problems, returns, and unsold stock sitting in inventory.
This won't happen with HTC and Sprint with the Evo because this phone certainly hasn't been rushed to market by a floundering company not able to control it's own production, inventory, and quality.