Well, as a member of "they," I'm glad you asked!
The SharePoint Server 2010 Software Development Kit (SDK) online documentation was refreshed on June 28 and I'm happy to announce that as part of the refresh, the Excel Services JSOM documentation was also updated--in fact, it's been completely revised.
Now, the topics for each object and function in the JSOM have full documentation, including Parameter info, Return Types, and Remarks. We even tossed in Code Samples for good measure!
Note to aspiring developers reading this: you no longer have an excuse not to create amazing solutions using the Excel Services JSOM!
The Excel Services JSOM documentation is here. Make sure to leave feedback! You can do so using the feedback control at the top of each topic:
P.S. Why are you still reading this? Shouldn't you be looking at the revised Excel Services JSOM content?