Don't be so quick to judge. There are still people out there who live in places where broadband isn't available, yes even in the US. One of my good friends is in that boat. He's been trying for years but he simply can't get the access.
Anyway, I'm thinking multiplayer would be okay. We played with a guy last night whose ping was over 600 at all times, and damn near 2000 at some points. We (a local friend of mine on the west coast US, also on broadband) made it through an entire game without issue, and despite the lag pausing the game a bit too often when it was at its worst, he never dropped and it never became a problem. Wish we could test this with actual dialup (the guy was in the UK and had forgotten to turn off some torrents he had running), but from what I saw in that game, dialup should be fully possible. This was a 3v3 match on a medium map with versus 3 CPU opponents.
Anyone else confirm similar results?