As an attendee, I'll be honest and say I was there for the free stuff. It was a bit disappointing we only get watches this year. Would've liked a new tablet or something. But oh well. Yes, yes its free, but I/O has always been known for gadgets.
The purpose of the conference is for people to be better developers not free stuff. Google bribes attendees like a parent bribes a child with a promise of a present if they eat their vegetables. Also the idea of gifts are to get developers do to program due to new API versions or new form factor of devices.
2008 no giveaways
2009 Android 1.6 phone
2010 Android 2.3 phones two models depending on your location and thus the carrier type
2011 Android 3 tablet, 1st gen arm chromebook, lte hotspot
2012 Android 4.0 phone, 4.0 tablet, chromebox, nexus q
2013 Chromebook pixel showing off high end hardware can work for chrome and developers should see chrome as could be nice not just cheap.
2014 Two android wear watches
Like I said first person problems about complaining of the quantity or quality of FREE stuff. Google's gifts are very logical, they gove their kids chocolate milk so their kids get vitamin d and calcium, instead of soda which is what the kids really want.
Love Google IO for the stuff, come for the learning.