They are not freely available as in: first you have to register with Apple as a developer and you can only view them after you log in with your developer account.
I'm not even sure if they are free. There used to be a way to become register developer for free, at the lowest tier, but didn't Apple change the rules in the last year or so and you have to pay $99/year for mac developer program and $99/year for iOS developer program, so to access all the videos you actually have to pay $200/year?
Yes, it's terrible that Apple wants you to register for free to download the videos about developing for their platforms from their site; they owe it to you to provide the videos without a login, which is indeed free.
All of the videos are available without paying Apple anything.
There's still a free tier; and all of the videos are accessible to those who are not members of the paid programs (but are registered under the free one).
The $99 registration fee is not for the videos (that's for app store distribution, access to the betas, restricted documentation, etc). You can register for free at http://developer.apple.com/programs/register/ and that'll give you access to the WWDC session videos.
I'm not even sure if they are free. There used to be a way to become register developer for free, at the lowest tier, but didn't Apple change the rules in the last year or so and you have to pay $99/year for mac developer program and $99/year for iOS developer program, so to access all the videos you actually have to pay $200/year?