Sony uses the method similiar to PS2.
PS2 only have 1 laser (2 lens in 1 laser). One len pick up CD and one len pick up DVD.
PS3 does the same stuff, (3 lens in 1 laser) One len pick up CD, one pick up DVD, and last but not least pick pu Blu Ray.
Although, making seperate lens are more recommended such as 3 seperate laser lens but Sony want to keep the cost down.
2 seperate laser lens are found in some dvd players that are inepensive nowadays.
Such as Panasonic dvd players, and possibly Pioneer too. Not sure about Sony though but I think they uses 1 laser for their bottom of the line dvd player...
the benefit of seperate laser lens for reading ead type of disc seperatedly are longivity of laser, better laser pickup which can read dirty disc, scratch disc easier...
but either way works just fine...