San Francisco is expensive. Traveling there is expensive. WWDC tickets are expensive. Many developers in attendance won't have a company to pay for it all. Sure, deductions on your taxes help, but you are still paying a big chunk of money to go. I tend to be pretty frugal myself and much of what Joe talks about is stuff I would recommend. Devs like to save money and make things as efficient as possible. Use Joe's recommendations to apply that thinking to WWDC.
I would also add that travel hacking is a real thing and totally legitimate. I have signed up for several credit cards over the last few years and have amassed a decent amount of points. Our family is doing a Disney Orlando trip this summer and we have no airfare or hotel costs. We also are paying for much of our tickets with points. If you don't have the points already, it's too late to get them for this year's WWDC, but keep it in mind for the future.
Note: You must be disciplined and pay off each card each month along with tracking your expense to meet the minimum spend to get bonus points.
WWDC on a Budget by Joe Cieplinski