You used to have to buy the PDC sessions on expensive DVDs for hundreds of dollars. Even after Channel 9 had been up for years.
The reason you can now access them for free is because Google made their sessions for Google I/O free and live streamed them. Before the days of Google there were no Express Editions of the dev tools either.
I won't be going to another Build, but I will be going to a lot of other dev conferences this coming year in the area and norcal.