Because you're using Windows 7. When you'll put in this HDD in your upgraded system, it will work and system will boot with drive and existing Windows 7. You can then install new drivers.
Else, you can always clean install the Windows after upgradation. In case you are going to opt clean install then yes, you'll have to install other softwares as well.
Most of the times Windows install the drivers or atleast try to install, however, you should install the drivers after windows installation is completed.