Maybe I can explain it a little better... Technically they both fit on a 'businesscard CD.. as they usually hold 120MB.. and netinst is a little over 50MB while the Businesscard is only like 15MB.
The Businesscard does nothing more than run through the installation routing and connect to the net to download EVERYTHING.
The netinst disc will install the very minimum base system from the disc and then reboot to continue installing software from the net. It is technically possible to install a totally minimum system without internet access using the netinst. Disc... I would think their 2 names should be reversed.. but it works nontheless...
As a side note, I have always had better luck with the netinst disc than the businesscard for some reason. Sometimes when I reboot after the base install from the businesscard disc, it can't bring up the ethernet connection. I have never had this problem with the netinst disc.
Hope I cleared it up, good luck!