Because the invite says to come see what they have for iOS and OS X. Did you read it?
Yes I did.
What I'm saying is when has WWDC logo represent a radically change in Apple's product/interface designs?
WWDC logo evolution
WWDC 2006 & 2007 were pretty similar with Apple logo, WWDC06/07 and a dark background.
WWDC 2009 & 2010 were pretty similar. No Apple logo and huge WWDC title with apps.
WWDC 2011 has the apps design from WWDC 2010 but has a new huge Apple logo that is made up of apps.
WWDC 2012 has the Apple logo design from WWDC 2011 but no longer has apps and now just blank, colorful icons. Plus it has no background.
WWDC 2013 has the color blank icon design from WWDC 2012 and also has no background.
What I'm saying is none of them is radically different from the previous one. All incorporate somethings from the old ones and add some new layer of design.
I dont think the WWDC 2013 logo is an accurate representation of what to expect in iOS 7. I mean I want a new UI but supper skinny text and then a slew of bright, rainbow colored icons.
iPhone 5 for WWDC 2011?
I mean saying the icon looks different = updated iOS UI is like saying I see a 5 in the logo = iPhone 5 early update.
Apple doesn't really give hints at what to expect for WWDC with their logo, its more for their product events. For example iPhone 5 and the 5 shadow.