No, 480p and 576p are equivalent to each other, but are the resolutions of NTSC and PAL, respectively. NTSC has 480 lines but refreshes at 60 Hz. PAL has 576 lines but refreshes at 50 Hz. There is also PAL60, which is 480p and refreshes at 60 Hz, but uses the PAL colour set rather than the NTSC colour set (PAL is superior in terms of colour).
Anyway, I suspect that they're using a loophole, to call it HD. Strictly speaking, 720p and higher are "high definition", not "HD". "HD" is just an abbreviation. So long as they don't actually claim "high definition", they can use "HD" as much as they want. I also don't think that the term "HD" (or "high definition") is legally enforced - I think it might only be a standardised term in the industry.
well it should be because i'm sick of sub par picture on my bought and paid for and made me broke tv. I do have direct TV but some of there hd channels piss me off and this I think is the best of the best with HD. So I think HD should be legally enforced. I like to use my Samsung tv's power.