IMHO, It really depends on what the company feels works best.
Examples:
Have a world changing event to explain why things work differently now. This worked very well for Shadowrun 4E. They advanced the timeline 5 years, declared the world suffered a computer crash and remade the whole world wireless. Granted, this had little to do with the system, but it was, none the less, a new edition.
"Retcon" the background so that things always worked the way they will in the new edition. Exalted 2E did this BEAUTIFULLY! Very little was changed officially, but alot of the gaping holes were filled in with much needed retcon.
Scrap the setting and start a new one tied to the new edition. Traveller does this with EVERY new edition. Some go over well. Other's ... the lead balloon. Some convert over to the new system. Others, well ... there are still 1E Traveller grognards as well as GURPS Traveller grognards.
Completely ignore it. The system shouldn't define the setting. Its common knowledge that Exalted's system was a tweaked version of the oWoD system (Storyteller System). In 2004 when WW launched the nWoD with a brand new system (Storytelling System), Exalted was not changed over and neither was 2E's version changed.
So, my best advise is, "Whatever you think (or your market research tells you) your target customers will buy."