Well, Wii is aging, and Microsoft and Sony are doing big things for their consoles. I see ads everywhere for Xbox and Playstation, but no more for Wii.
MS and Sony also have new control schemes coming their way, while Nintendo isn't doing anything drastic. Sure you can say a TON of games are coming out this holiday, but the only people that are excited are the people that already have Wiis. So many games came out already for the Wii since 2006, so how will these new releases create more sales?
My guess is that E3, Nintendo actually catered to the core. Many happy fans, including me, were estatic about the announcements, but what about the "blue ocean" audience? They had Wii Party, and...? I don't think a lot of people were thinking, "Well I don't have a Wii yet, but the E3 made me want to buy one." Basically, the E3 catered to the people that already have a Wii IMO, while Microsoft and Sony attempted to attract new audiences.
With that said, Nintendo is NOT doom and gloom. Wii will hve slower sales, but they seem like doom because we're used to 250-300K weekly, which is actually insane for any console. Nintendo also still has options left to attract audiences. (Good God, they need a player's choice. I still see Twilight Princess for $50)
Long story short: Yes the Wii sales dropped, and it's sad. But it's also normal, and the other companies have done major changes to take away some sales. Wii fans (me included) should not cry over the sales, but accept the fact that Nintendo is no longer invincible in the home console department.