What if they are staring at the screen for 3 minutes, pondering their next move?
They should say "thinking" or something to signal that they're actually there.
I had a game just recently in which I was one click away from winning the game and my sister's 1-year-old son decided to shut my computer down without a warning. I restarted and made it in time, but more than I felt good for winning the game, I felt bad for making my opponent wait and it most certainly wouldn't have been my opponent who I would've been angry at if I had been forced to resign, but my parents who were keeping an eye on the kid and apparently couldn't have cared less about whatever unsaved work I could have had.
Waiting is boring as hell and I have always forced and will continue to force all of my opponents to resign as soon as it's possible, unless it happens so fast it's obviously a bug or my opponent has told me in the chat that he hasn't stopped playing even though for any reason he's taking a while (and expect the same thing to be done to me). Otherwise, for all I know, my opponent could have just decided to stop playing, could be experiencing a blackout, could have had a heart attack or whatever - that's going to be an eternal wait for me and in any of these cases, his primary concern wouldn't probably be winning a single funny game on Isotropic. And this is an especially good reason to force resigns because the first of my sample reasons for being silent is probably extremely common.
Also, while I believe that nobody would be actually doing it anyway, it's a good thing that you can't just come here and read a long and detailed strategy guide during a game without the fear of being forced to resign. Checking the opening guide or something small like that is still possible, though, but I don't think that's a big problem.