This is a bit misleading for people looking to start your typical startup (using PG's definition of 'startup'). All those startups you read about raising money - want to know how many of them are C-corps? Just about 100%.
One thing that many people don't realize is that for many startups, those pass-through tax benefits of LLCs and S-corps are largely illusory, since they're not going to be profitable at that stage anyways.
Starting off as an LLC means you're going to introduce delay when you start raising money (unless you're really on top of things and convert in advance of fundraising), which introduces deal risk.
Yes, there is double taxation on income from C-corps, but most startup founders aren't in it for the salary / dividends, they're in it for the eventual acquisition / IPO (or these days, private market sales). Gains for QSB stock held more than 5 years are now tax-free under Section 1202.
There's a whole bunch of reasons why companies end up as corporations - not just the QSB stuff. Main street small businesses are often fine with LLCs or S-corps. Startups (as defined by PG) should really talk with an experienced startup attorney before going the route of an LLC or S-corp.
LLCs are relatively easy to convert to a C-Corporation, as are S-Corporations (which can automatically convert to C-Corporations). C-Corporations are generally very difficult and very expensive to convert to other forms.
So, C-Corporation status is great if you know that you will be getting VC funding. It's not so great if you only think you want VC funding, and it's a relative nightmare if you are trying to bootstrap.