This was my point too. Sandboxing is something affecting all sites new and old. Really what people are calling Sandboxing is just the same thing many experienced after Florida. I think Google has spread out its filters to cover a broader range of terms. Or if you don't like the word filter it has applied a new weighting system that favors directories, links out, and strong local rank over content and pr.
You can beat this system by working toward building better links and designing for the new "directory is king" Google.
I believe the reason people feel that it is a new site penalty is due to the lack of link depth that newer sites have compared to older established sites. Generally it is easy to build pr; just have a bunch of sites and link them together and puff pr. However, local rank is harder to establish because the links you get can't be affiliated to you. Therefore it is a slower process and new sites would need time to build these types of non-affilated links.