7500 is actually reasonable for vehicles that are not used hard. Such as a highway commuter. The 3000 mile thing was a combination of the old oil and car technology in the old days, along with marketing. More oil changes means more money for oil companies and those who do the changes for people. Todays modern, efficient vehicles, combined with better oil technology, cars can go a long time under normal situations.
Of course most of us that use this site are not "normal'.
We virtually beat the snot out of our vehicles in the mud, rocks, and other off road situations, as well as towing and such.