I get why you're upset, but the other side of the coin is that for a lot of people, going out to Gencon requires a much greater investment of time and effort than pre-ordering. For someone who bases his or her decision to go to the con in any part on the availability of OoTS content, it's hard to begrudge someone who's actually willing to go outside, braving sunlight, possibly airports, and even more dire, airline food, their right to purchase slightly before we receive our product by mail.
IMHO, if being a lazy, on-line shopping, pre-ordering fan means I might get product a little later than someone else...well...that's the price of convenience. YMMV...just my opinion.
Not to mention paying for all that just to for the chance to stand in line to buy the book. I'm pretty sure paying the shipping costs on a pre-ordered book is a wee bit cheaper than all the expenses to get to and into the Con. A pre-ordered GenCon ticket for 1 day is something like $35/$40 if I remember correctly from last year. (Just for some added perspective, not to beat a dead horse. )