Price increases and market position are different.

I bought a new Camry in 1991 for $12000 and a new Camry in 2007 for $23000. True, the 2007 is 3X the 1991 version.... but they are both Camrys.

Also people may not like "having to settle for less" so having one "model line" with different "trim lines" softens that blow. You cannot get the customer to buy if you make him/her feel bad about their purchase.