Thats not always the case, some people just buy a pc, for a lot of reasons, you have no idea of how manys are still stuck with 775/AM2/AM3 dual athlons, or even older. Or in some cases worse, the shitty good for nothing 2650/3850 that they brought as new...
If someone has a i3/i5/i7 will probably go and buy a dgpu, althought i whould not recomend a R7 240 since its slower than the A8-7600 IGP even on DC 1333 ram, and it probably not be much of an upgrade even to a G4500 now.
Anyway thats a minority, a lot of people are upgrading from lesser things than that, or just want a new pc, maybe they are not upgrading anything.
HD510 and HD530 makes an important improvement on low end, belive me, specially compared to other offerings like the 5150/5350/7300/7400 taking in consideration cpu/igp, the A8-7600 will more than likely end up better thought, but maybe not on all games.