Some apps with not output video to a TV monitor unless you have a supported video card. I use Avid Media Composer but I can't watch it on a TV ( live video preview and not a pc screen ) due to my desktop graphics card ( Radeon 5850 ). I can spread the app in two monitors at once of course but PC monitor colorimetry is not the same as a TVs. So pro-cards do have advantages....but money is always the sticking point.
I would love to have a Mac with FCP and an AJA/Kona3 card to work with but....the funds are just not there. If you are working on video files only and don't have to output to tape of any sort a "lowly" pc graphics card may suffice or now. Once you get good with your apps and you can get money from jobs it becomes more possible to purchase a better pro card.
Like some folks said here look at your product websites ( their forums too of course ) and see what they like you to use.