neither of those are the 550w version but if the 650w is anything to go by:
then mururoa is probably correct about the internals of the 550w.
Yes that's a bit cheeky if they are doing that

The HX versions still seem to get good reviews though so they are still good value for money if in testing they are coming out better than some more expensive PSU's.
Seems this review here states the Rosewill Capstone-550M PSU is basically the same PSU as the SuperFlower Golden Green HX 550W "80 Plus Gold" Power Supply - Black
Manufacturers Code:
SF-550P14XE (HX)
http://www.hardwaresecrets.com/article/Rosewill-CAPSTONE-550M-Power-Supply-Review/1584/1
They have more than one PSU with the same internals at superflower :-
http://www.super-flower.com.tw/products_detail.php?class=2&sn=8&ID=42&lang=en
http://www.super-flower.com.tw/products_detail.php?class=2&sn=18&ID=108&lang=