It is only " 7/8 seater " is a common thing btw Ertiga & Xylo. I own both the cars & can say each one is designed for a specific type of purposes.
Xylo :
1) Designed for people who wants to upgrade from sedan/Hatch to a SUV at tight budget (Model D2 & D4).
2) Tour operators who also have tight budget & need FE (Model D2 & D4)
3) People who own Scorpio/Safari/Bolero & needed change (Model E4,E6,E8)
4) Generally driven by well built persons or drivers. Clutch & gear are heavy to operate.
Ertiga :
1) Designed for people who wants to upgrade from sedan/Hatch to a SUV(or like) at tight budget (Model LDI/LXI )
2) Designed for people who need a " soft to handle or a car like SUV "
3) Designed for bigger family who need car like vehicle for 7/8 persons & not a SUV.
4) People who need a SUV like car(Innova) but a compact one for city driving & FE.
5) Designed as owner driven car. Generally white Collar people. Clutch/gear are soft to handle.
See my latest post on Ertiga
http://www.theautomotiveindia.com/forums/ownership-reviews/7221-maruti-suzuki-ertiga-zdi-bought-ownership-review-41.html#post181517