The way I see it is this: Primarily, it's the same as people have said above. It's not fair for the same people to get the good spots to sit every single week! Conspire with a friend or two to have them grab good spots first, to institute a pattern of rotation, or just openly start said pattern.
Now, as the host/ess, if this was the occasional one, it would be expected that you forgo having any sort of reserved seat. But this is something that happens every week for what, ten weeks, more if you do a last-season recap? And you're on your third year now? It goes from just being you hosting a gathering, to you doing them a favor as well. You provide them your home, a nice TV to watch it on, the use of your facilities, perhaps food/drink, and for some of them, the only legal way to watch the show, especially before they get spoiled by someone at work.
To say, "Guys, after three years, I declare myself the Queen Of This Seat, and y'all need to start taking turns in your peasant spots" is not unreasonable. Although while my friends would enjoy the way I phrased it there, you might need to rephrase it.
Summary: Three years, and the same people are still sitting on the floor? Start mixing it up. And given the circumstances, I'd say you have every right to secure your favorite week every week. Sheldon away, soft kitty.