Without working for the company, it is really hard to say exactly what the difference is but... typically different or more detergents and in a lot of cases the viscosity is a little on the higher side for it's stated weight among some things.... You will notice most of the high mileage oils won't have all the same OEM endorsements on them that their normal counterparts do. In some cases that is because it can no longer meet all the criteria. In others it is because they just don't have it certified. They tend to be aimed at a different market.
I have and always will maintain that routine oil change intervals at a reasonable mileage with basically any modern certified oil will allow the engine to outlast everything around it. There really isn't a need for it if you do that. Not saying it doesn't have it's place, but rather there is really no need if you do simple maintenance.