Reading Mini-wheats first post.
Was a bit
Not sure what made me feel that way though.
Anyway to serious business:
I think you massively overestimate the number of people without access to broadband. Here in the UK wiki tells me 18M have broadband, out of 23M homes. That's a large percentage. The only person I physically know without internet is my gran (she doesn't have a PC either. One day though, one day). Not to say that broadband can be really quirky (my new router hasn't emitted wi-fi for a good 3 weeks now, so my netbook is fucked in that regard) but I don't think requiring internet is a deterrent on sales in a technical sense. Unless Blizzard counts my gran as a possible customer.
I visit reddit a fair bit and they are very very quick to want to boycott things. And I've frequently pointed out how it's a very lazy form of protest. Boycotting is essentially not buying the game. You sit on the day of release and do nothing. Just last week I "boycotted" Driver. As you and others have pointed out there's no way to tell if a product has been boycotted unless it's en masse in a huge way. i.e millions of people. People who boycott games are probably of less consequence to publishers than people who pirate games. At least pirate numbers can be tracked.
I have being working on something along these lines for PXOD, essentially why boycotting is a shitty method of protest, and more viable methods of protest. I'm still working on it but essentially if you are upset about a certain element of a game:
1. Email the publisher/developer in question and express, in a clear and non-ragey childish way, what you are displeased with. Potentially offer suggestions and alternatives. Don't go "I dislike this, change it now".
2. Get in contact with game sites about this issue. They can have some clout, and at least a very public face, with which to bring up these issues.
Not to say boycotts are useless, but most are just randomly thrown out without any backing to them. And doing something through say a games site would have more chances of sticking than just some comments on a forum somewhere. As MasterDex's example with MW2 showed. While the boycott at the time may have seemed pointless all games since have had dedicated servers. If it was just tied to the steam group then it would have gotten nowhere, but it was picked up by gaming sites and it got discussion going and became bigger n bigger.
I think another reason why "boycotts" fail is because the issue at hand is annoying, but insignificant to the overall game. For example Deus Ex n Civ V have really really fucking annoying boot up screens/movies. But the games are really good so I don't mind. It's probably the same for many other games. The publisher has a real problem though if the issue is small and annoying, but the rest of the game hasn't got enough going for it. e.g Diablo 3 requires an always on internet connections, which I personally find objectionable, unnecessary and the devs reaction to it rather crappy. But it's fucking Diablo 3 so it's bound to get people just on that alone. From Dust requires always on internet too. The game itself is from ubisoft, a crappy port and short game. The scales aren't tipping in it's favour other than "it could be like B&W"