> Different chip's name but same architecture targeted to different users
> by marketing rules

Architecture is similar, but not quite the same:

RV570: 330M t., 80nm, 3 q., 12 t.u., 36 p.s., GDDR3
R580: 384M t., 90nm, 4 q., 16 t.u., 48 p.s., GDDR3
R580+: like R580, except 80nm, GDDR4
(t. = transistors, q. = quads, t.u. = texture units, p.s. = pixel shaders)