Agreed. The PS3 will certainly get a bump from those waiting for the slim, but I think people underestimate the extent to which people will go for the 360 and Wii because it's what friends have. We like to play with friends, and trade games, and talk crap about who got through which boss or earned what score/achievement, etc.
This really hurts the PS3 in America. In this case, an increasing lead directly influences furthering of that lead.
Surely this isn't all buyers, but it is definitely a factor. When my friends come over, we play 360, and it makes them want to play 360. My PS3 has sold a Blu-Ray player to them, but none of the semi-casuals want it. They think it's not for them, even though it's basically the same thing as a 360 in so many ways. They either have a Wii already or they bought/want a 360, depending.
Yep pretty much this, and it extends to online as well. With the 2:1 userbase advantage the question for online gamers becomes, Live has friends vs PSN has no friends. It also extends to the stores, when they walk in the Xbox 360 section is bigger so the console itself looks more successful too.