Based on the description on their site, the controller includes a built-in battery: "8.39 Wh Li-ion battery, 35+ hours of gameplay... "
That was disappointing for me. Specially condidering the Steam Frame's controllers make use of AA batteries: "One replaceable AA battery per controller, 40hr battery life"
AA Batteries might not be as convenient to use, but being able to replace them is a great advantage. All my Xbox360 controllers still work fine, but none of my PS3' Dualshock 3s.
The official docking station could be used to recharge (rechargables) AA batteries so the functionality could remain the same.
Yeah, but the AAs will still be around in 10 years. Until we standardize internal power cells and legally mandate companies use them, I don't really care how user-serviceable it is, by the time it actually needs a swap most companies are done selling it anyways and just want you to buy the next thing instead. At best you can get a shady third-party knockoff. Valve is slightly better in this regard, but I don't expect them to still sell batteries 10-15 years from now.
I think most people just use "user-serviceable" as a cope and never actually intend to service it, it just makes them feel better to think they can. They just throw it away and get a shiny new thing when it becomes slightly inconvenient.