That doesn't seem to be the case. I just made a free account quick to test this, and it won't let me access the betas without being a member of the paid iOS developer program.
Interesting. That works from my free account as well. However, I see no way to actually obtain that URL through the official site. Did I miss something? Is this a bug on their part?
By navigating from the developer center, or using a direct link you found elsewhere? I was able to download the release notes with a direct link but I couldn't actually find the link anywhere from Apple.