From the mention of a "variety of encodes" affecting their numbers, my interpretation of this figure is the average bandwidth used to stream a video to a subscriber, and in that case 2.55MBps sounds shockingly high for an online streaming video bitrate. 2.55MBps would put it a bit above over-the-air broadcast MPEG2 HD rates, whereas not everything on Netflix is HD, and I would assume they're using more efficient codecs than MPEG2. Especially since, from my past experience, I know that they have HD streams that are playable on sub-6Mbps connections.
EDIT: and as tedchs points out, the other provider numbers definitely reinforce the interpretation of it being Mbps: I don't think I've ever seen AT&T advertise a non-Uverse DSL speed of above 6Mbps, which wouldn't let it hit 1.5MBps.
I'd argue that deciding to name 8 bits a byte and making the abbreviation of the latter simply the capitalization of the former was an ill-considered choice, and has led to much confusion, consternation, and gnashing of teeth over the years.
We should adopt the telecom term octet, and just get rid of the term byte.
Then again "Megaoctet" doesn't quite flow, but there would be no confusion between a bit and an octet however you abbreviate it. We're still left with is deciding whether to multiply by 1000 or 1024 for each magnitude though.
Read my reply to tedchs, I believe he[assuming] is still reading the numbers wrong, including the mobile numbers.
I'm not sure about your numbers, as I'm finding a bunch of conflicting information online. From what I've seen, an HDTV quality stream would be around 2 MBps, but I've also seen numbers closer to what you're reporting.
It's conceivable to me that Netflix could do a quick speedtest that would exceed the video bitrate when testing your connection for HD-ness.
In any case, I might be wrong. Netflix should really clarify this. There are people arguing about the same thing in the comments to that article.
EDIT: and as tedchs points out, the other provider numbers definitely reinforce the interpretation of it being Mbps: I don't think I've ever seen AT&T advertise a non-Uverse DSL speed of above 6Mbps, which wouldn't let it hit 1.5MBps.