No reason you couldn't get the close to the same quality. You can set torrents to auto download most tv shows and even have them converted automatically to show up as recorded tv in windows media center. You can also use Hulu, Youtube and many other services to stream most of what is on tv in good to HD quality. This can all be integrated into a front end like media center. As for games, if your internet provider allows ESPN 3, then that's a great source that streams good enough for a tv. You can also check out justintv, which not only streams games in HD, but is usually doing out of market games. Check out sites like thegreenbutton, Hack7mc and even avsforum and they can show you how to integrate it all. Sounds like you've already looked at some of these sites.
I still have cable because others in the home won't let it go, but I'm pretty much ready to cut the cord. I use 4 OTA tuners, 1 QAM and 1 HD-PVR to record cable in HD. I have torrents automatically downloading and converting tv shows, races and sports to Recorded TV. I have Hulu and Boxee integrated into media center, and I use a program called macrotube to get Youtube HD and other streaming services into media center as well. Combine that with Netflix streaming and I rip all movies to another big HDD. Its all reachable to media center, but I hope to see it even more integrated. This is the future of TV, and like it already and never miss anything I don't want to. NFL games are mostly on networks, so OTA and/or QAM picks them up in better than cable or satellite quality anyway. If you don't have NFL Network, they have a $40 service that streams all preseason games in HD. I imagine Sunday Ticket will do the same at some point.