Not all devices support all streaming protocols and formats. I.e. their desktop player uses the proprietary SMPTE 421M codec (microsoft) which is not available (or efficiently implemented) on platforms where silverlight is not available (read: most of them).
Since many of these other platforms also use proprietary formats they end up having to maintain a range of different proprietary streaming servers, many of which presumably need to interface with their respective mothership platform services (XBox live, PSN, Roku).
Oh, and recently they have begun building their own CDN[1] which may add further to the diversity.
See also: http://gigaom.com/video/netflix-encoding/ and DRM schemes, esp. those detailed in content contracts (protip: big studios specify codecs, encryption specifics, etc.)
Different for each device based on how much power the device has. TVs have nothing for CPU power in most cases.
Since many of these other platforms also use proprietary formats they end up having to maintain a range of different proprietary streaming servers, many of which presumably need to interface with their respective mothership platform services (XBox live, PSN, Roku).
Oh, and recently they have begun building their own CDN[1] which may add further to the diversity.
[1] https://signup.netflix.com/openconnect