I think there's 2 reasons why Sling has an n95 client:

1) Orange or 3 in England bundled a slingbox and n95, and likely payed for development
2) The CEO of Sling Media is an n95 fan. He got to demo an early n95-3 a few months before it came out, showing off to Om Malik.

However, it has been rumored they are introducing a sling client for the iPhone. I could see a port to the Linux world at some point, but don't look for a GPL'd build. It does work in WINE now, but you have to load up some Windows Media player plug-ins.