I just heard back from Sonos Tech support.  Here is their explanation:

“Some of our developers and other engineers took a look at the bug I entered for your issue on how the Arc is failing to turn the TV on.  They confirmed that the Arc does communicate over CEC a little differently by sending the command via a broadcast instead of directed message to the TV and this specific TV at least is unable to support that message type. 

Unfortunately this means that this is not likely to change and your Arc will not be able to power that TV on as the Beam did.”

Ugh!  Needless to say, the Arc is not compatible with my TV set.  Do your research before you buy the Arc.  I imagine that this problem happens with many TV sets.  If I had to do it over again, I would stick with the Beam.  Not worth paying $799 for a system that only sounds marginally better than the Beam.  Maybe if I was buying a new TV with e-arc would I consider it to be able to use Atmos.

If you don’t have a TV with e-arc, BUY THE BEAM.  DON’T WASTE YOUR MONEY ON AN ARC!!

Ken

Honestly, I consider CEC controls to be more of a bonus feature of the Arc or Beam rather than an essential.  I also find CEC controls to be rather unreliable, as each manufacture can chose to implement the feature differently. 

I’m actually surprised the feature worked between the Beam and your Samsung TV.  My understanding was that that Samsung only heeded the turn on/off command if the input was set to the ARC input...which you would never do.

There are other ways to turn on/off a TV besides CEC controls though.  You can configure a harmony remote or fire tv  to turn off a TV by voice.  And since your TV is a samsung smart TV, you should be able to set it up with smart things to allow on/off voice commands.  The latter is what I do.  In fact, I wouldn’t be too surprised if your Beam never actually turned off your TV via CEC controls, but you had one of the other methods in place without realizing it.