I finally installed Yosemite on my iMac Core i7-870 (2010), and Netflix works fine in Chrome, but not Safari.
Note that Chrome first threw up a message saying:
WidevineCdm was indeed already there, but I updated it and now Netflix works in Chrome (but still not in Safari).
Core i7-870 is 2.93 GHz Lynnfield.
Interesting. I re-installed Silverlight, and I get the impression that Chrome doesn't use it anyway, but now Netflix works on Safari.
In Safari when I'm viewing a video, the HD icon is there, and lights up when HD is playing (which usually requires a short period in SD to buffer HD). Before I installed Silverlight though was a screen telling me to install Silverlight.
In Chrome when I'm viewing a video, there is no HD icon at all, but I do get HD playback (after the initial buffering period). This is the same before and after I installed Silverlight.
Furthermore, when pausing or going back to certain menu screens, in Safari it's just static text, but in Chrome, there are motion animations. For example, when the Netflix text logo is displayed before watching videos, in Safari it just appears, but in Chrome it zooms.
IOW, they seem to be using different code for rendering menus, with slightly different interfaces and slightly different behaviour.
I'd be curious to find out what the interface is like on Safari on a newer machine without Silverlight. None of my Macs are Sandy Bridge or newer.