Interestingly enough LCD-equipped Lumia's like the 920 and 830 work just fine with it while MS deemed AMOLED-equipped Lumia 930 and 730 as incompatible which is interesting.
Presumably the type of display (AMOLED, LCD) only affects how much power is drained from the feature for the screen portion only - AMOLED being considerably lower due to the drain involved for displaying black
I think the main issue would be the graphic chip and related hardware driving the display as to whether or not the feature can be enabled. i.e. supporting a low powered state
Samsung's "always on" feature was only made possible by making everything run in a low powered state, reducing the frame rates and limiting colours used to 8 with active switching if more is needed. Also disabling the feature if sensors detect you're not going to be using it, i.e. in pocket.
If i remember from my 1520, glance would turn off after a period and I would just have to sweep my had over the top of it to get it to show again.
I would therefore assume Nokia made use of certain low energy states and have certain sensor requirements they deem to make it worthwhile. Display's power drain per pixel isn't necessarily the biggest factor if you dont have a driving chip that can run on a phone's sleep state etc