I'm surprised and a bit skeptical that every CA (except for one) randomizes serial numbers without it being published in a standard or guidance document somewhere. Best practice usually has something worse than a (n - 1) distribution.
As long as you purchase your certificate from a CA well placed in the major browser vendors, you're good to go.
Edit: Here's a list of Mozilla's included certificates: http://www.mozilla.org/projects/security/certs/included/