I don't take all my gaming advice from executives and vice-president's either, and I never said that I did. But they do have the power to direct where future investment will go, and they make these decisions based on the revenue earnings of games already on the market.
I confess my comment was a little snarky. Still, my understanding is that there are vastly more people who play single-player games than there are people playing multi-player games. People posting to online gaming forums are more likely than most to be multi-player gamers, so you'll get a biased overall opinion from reading forums.
I don't think single-player modes are in any danger of becoming unpopular. Consider who those quotations are from:
Sony Online (who have EverQuest and a whole array of other online titles to push).
EA's former VP of online gaming.
An XBox exec, ready to talk up their XBox Live capabilities.
These are all people with an agenda. I really don't think they form the basis of a balanced opinion. You're right that they undoubtedly have some influence, but they only affect the developers under their own umbrellas, which (to mix my metaphors) is but one slice of the pie.