I figure it's a classic case of media laziness...if you notice, there are always pundits who compare contemporary world events to well-known events of the past, not always accurately. Comparing the inauguration to Woodstock is the same as comparing any current right-winger to Hitler, or (my personal favourite) the total inaccuracy of referring to something as being "on acid" (i.e. "this TV show will be like Bonnie and Clyde ON ACID")...used to denote something that is akin to another, similar setup, but Wild and/or Crazy (also Unexpectedly Cool). There's a great British comedian called Bill Bailey who does a whole rap on the inaccuracy of "_______ on Acid" that you should check out. But I digress.
It's laziness through and through -- we put certain historical events or people on these pedestals of importance and then use them as common media-tagged landmarks to which we can apply everything else, ever. ANY large gathering of people in this day and age that is remotely jovial and non-violent would be compared to this false notion of Woodstock as being one big love-in (which it wasn't). I found it funny because when I heard the commentators recalling Woodstock with such nostalgia, all I could think was "You mean the inauguration is a poorly-planned music festival that will ultimately result in several deaths due to an unforeseen rainstorm / mudslide where several people will die of malnutrition and drug overdoses? Cool!"
Boring, stupid pop-culture hype. That's all it is.